Vaccination

SYNONYMS.—"The new inoculation;" Fr. Vaccination; Ger. Kuhpockenimpfung, Schutzpockenimpfung; It. Vaccinazione; Sp. Vacunacion.

HISTORY.—Before giving the history of vaccination itself (meaning by that term the intentional inoculation of vaccinia for the purpose of protecting the subject against small-pox), it may be well to devote a few words to a practice that preceded it—that of the intentional inoculation of small-pox (or simply inoculation, latterly called variolation). In very early times various Oriental peoples became aware of the fact that small-pox might be very decidedly mitigated by inoculation. This was practised in various ways, all of which may be reduced to the process of inserting small-pox virus into a solution of continuity. Lady Montagu, the wife of an English ambassador to Turkey, brought the practice back to England with her, where it soon made its way into popular favor, and whence it spread rapidly over Europe and America. Thus contracted, small-pox was shorn of a great part of its terrors; the eruption was usually trifling in amount, and in every way the disease was mild as a rule. Still, the mortality was something worth considering, and, worse than that, the inoculated disease was communicable by effluvium, so that an inoculated person had to be secluded carefully for fear of spreading the disease in the ordinary way. In all cases, too, careful medical treatment was thought necessary. On the whole, then, while inoculation was undoubtedly a boon, it was fraught with many grave perils. So great, indeed, were these perils, and so thoroughly were they appreciated, that the practice was interdicted by law in most civilized countries so soon as vaccination had become established in popular favor.

In several European countries the common people—at least those of them who had much to do with dairies—gradually became aware of the existence of the disease termed cow-pox, and of the fact that those individuals who had accidentally contracted it were rendered proof against the infection of small-pox. There is even fair testimony to show that some of these people, particularly the English farmer, Benjamin Jesty, relying on their observation to this effect, employed intentional cow-pox inoculation as a protective measure. These facts, however, do not detract in the least from the credit that all Christendom has awarded to a man who subjected the popular impression in question to the test of scientific investigation, proved its truth, and demonstrated its value to the world. That man was Edward Jenner, an English country physician. It was in the last quarter of the eighteenth century that he entered upon his course of inquiry, and on the eve of the present century he published his demonstration to the world. It was not a discovery; it was not an invention: it was more than either, "a matchless piece of induction," to quote the words of Mr. John Simon. Filled as he must have been with the consciousness of his great achievement, Jenner set this good example to all investigators: that he did not make haste to convert the world; he first convinced himself. It may almost be said, indeed, that, like Minerva from the head of Jove, the rational and perfected practice of vaccination sprang complete from Jenner's hands. Doubt and ridicule he had to encounter at first, and afterward envy and detraction; but the force of his facts and the symmetry of his deductions were such that the new inoculation soon spread through the broad world, and has ever since maintained its sway, save with a few fanatical scoffers.

That vaccination really does protect against small-pox observation has taught the whole civilized world, if we leave out of account the few conscientious and intelligent doubters (made such, doubtless, quite as much by the extravagant statements often put forth by those who from time to time think it incumbent on them to defend vaccination, as by their own misinterpretation of facts) who are to be found associated with the noisy little body of actual opponents of the practice. One of the most injurious statements ever made in the advocacy of vaccination is, that it always protects if properly done. When one of these illogical defenders of that proposition is confronted with an instance that disproves his assertion, he falls back on the allegation that in that instance the vaccination was not properly done. The manifest absurdity of such an argument strikes the doubter most forcibly, and inclines him to say to himself, Falsus in uno, falsus in omne. Unbelief founded on this ground would never have arisen if the plain truth had always been adhered to: that the protection afforded by vaccination is not invariable, and that very often it is not permanent. In the infancy of the practice these facts were not known, but it is now many years since they became obvious to every fair-minded observer. The misapprehension of facts lies chiefly in the false deduction from the circumstance that the great majority of cases of small-pox occur in persons who have been vaccinated. But the explanation of this is very simple. Suppose that, of one hundred persons vaccinated, twenty fail to be protected permanently; that all persons not vaccinated are unprotected; and that throughout the civilized world the proportion of vaccinated to unvaccinated persons is as ninety to ten. Making no pretence of arithmetical accuracy, it may certainly be said that all these suppositions are well within the truth. It follows from them that in a community of ten thousand persons there will be nine thousand who have been vaccinated, and one thousand who have not. Of the former, eighteen hundred will have failed to secure lasting protection. Therefore in case of an epidemic there will probably be a proportion of eighteen cases of small-pox in the vaccinated to ten in the unvaccinated; and yet this should not obscure the fact that of the nine thousand vaccinated more than seven thousand were absolutely protected, whereas of the one thousand not vaccinated not one could escape the disease if exposed to it. When we add the further observation that of the eighteen hundred cases of small-pox among the vaccinated not more than thirty or forty would probably prove fatal, while of the one thousand cases in the unvaccinated about two hundred would end in death, we have a striking demonstration of the efficiency of vaccination. As a matter of fact, statistics show that the figures here given err rather in allowing too little than in asserting too much in favor of vaccinal protection.

The question naturally arises, Why it is that vaccination protects some persons and does not protect others?—reference being had, of course, to permanent protection, for it is exceedingly rare for temporary immunity to be attained if we exclude those instances in which the variolous infection has taken place before the operation is resorted to. This question cannot be answered with any certainty, but various theories have been brought forward, some of which call for notice.

In the first place, it has been thought that the revolution of the system termed puberty was fraught with such a radical change as to do away with the mild modification due to vaccination. While this theory has an air of plausibility, it seems to lack proof and not to be upheld by analogy, for we do not find that children who have had scarlet fever, measles, and the like often undergo those diseases a second time on arriving at the age of puberty.

The only remaining theory that our limits will allow a consideration of is that put forward by Marson of London, that the degree and duration of vaccinal protection are proportionate to the perfection of the vaccinal lesion and to the number of insertions made. In a large experience with small-pox Marson found that the disease was more fatal among those whose vaccinal scars were imperfect or few in number than among those who bore evidence that several pocks had been produced and had run a typical course. As to the influence of a perfect evolution of the lesion, but little doubt can be entertained, for we have already seen that in some instances its course is so different from what it should be that no protection whatever seems to result. When we come to consider the number of the pocks as affecting the degree or the duration of protection, however, an obvious source of fallacy arises in the fact that we cannot always be sure that some of the scars on a person having a number of them were not the products of a repetition of the operation several years after the first—that is to say, a revaccination, the efficiency of which in restoring lost immunity is now well established. Nevertheless, as long as the doubt remains the best course to pursue seems to be to act as if Marson's theory were in all respects correct, and vaccinate by multiple insertions.

We have, then, no positive means of ascertaining who those persons are that are likely to fail of lasting protection, or how long a time will elapse before the cessation of their immunity will take place. The only safety lies in revaccination. But after how many years should revaccination be resorted to? It has been thought that this question might be settled by noting at what age, or at what period after primary vaccination, large numbers of people became susceptible of revaccination. This test, however, is not altogether trustworthy, for a renewed susceptibility to vaccinia by inoculation does not necessarily imply that the liability to take small-pox by effluvium has been regained. If it did, modified small-pox (varioloid) would be far more common than it is, for it is certain that revaccination can be made to succeed in a very large proportion of children long before they have reached the age of puberty. The fact is, contrary to the notions of the last generation, that success in revaccination is the rule, not the exception. Formerly it was not expected to succeed, and therefore no special pains were taken to ensure success.

Definite rules cannot be laid down as to the time that should be suffered to elapse before vaccination is repeated, but in the great majority of instances safety may be attained by revaccination every five or six years, and always in the presence of an epidemic, regardless of the lapse of time; also whenever one's mode of life is to undergo a noteworthy change, as in emigrating to a foreign country, on entering the military service, and the like.

To sum up, then, vaccination almost invariably protects against small-pox for the time being; generally for a long term of years; sometimes for a lifetime. Often the protection is absolute; as a rule, it is very nearly so; in rare instances it is trifling. In general terms, it may be said that it is scarcely less protective than variolous infection itself, for death from a second attack of small-pox is by no means rare. Here the question comes up: Is vaccination less protective, either in degree or in duration of effect, than it was at the time of its adoption? Given a typical vaccinia, we may unhesitatingly answer, No; but do we now so invariably produce the disease in all its essential features as was done in Jenner's time? Yes, provided we use proper virus and employ as much care as was taken by the older physicians, who, trained to the practice of variolation (the inoculation par excellence of bygone days), did their work with a gusto now seldom witnessed. But there was a time, now happily at an end, when it was not easy to obtain thoroughly good virus, and when, therefore, the result was apt to vary materially from the standard. This may be conceded without entering upon the vexed question of the general deterioration of the Jennerian stock of vaccine.

Besides immunity from small-pox, there are one or two sequelæ of vaccinia that deserve mention before we proceed to consider what it is better to class as complications. In the first place, vaccination has been supposed to confer temporary protection against whooping cough. The writer is not aware, however, of any precise data going to prove either the truth or the falsity of this supposition.

Secondly, by virtue probably of the inflammation that attends the evolution of the vaccinal pock, vaccination practised in the immediate neighborhood of a small nævus often cures that blemish, and it has been done for that purpose in many cases. It has no advantage over many other measures, however, and there is the disadvantage that the nævus may so mask the pock as to give rise to some doubt as to the satisfactory character of the latter. The practice, therefore, is not to be urged.

COMPLICATIONS.—These are local and systemic. Those of them that are at all serious are rare, and can generally be traced to fortuitous circumstances.

Inflammatory complications are usually due to undue traumatism at the time of the inoculation, to injury of the pock, or to the previous existence of a cutaneous disease or of some dyscrasia. Dermatitis is the most common. It is usually a mere erythema, but in some instances lymphangitis, lymphadenitis, phlegmonous inflammation, with diffuse suppuration, may result. From injury of the pock ulceration and gangrene may take place, and septic absorption may follow in their train. These complications are to be treated as if they had occurred from any other cause. Generally, the mere vaccination is not responsible for them, but in some instances putrescent vaccine may be adduced as their source. In such cases the complications, if they can still be called so, are apt to make their appearance long before the pock matures, even within forty-eight hours of the vaccination. Inflammatory complications supervening on the full development of the pock may invariably be set down as due to some cause not connected with the quality of the virus employed.

An undue amount of dermatitis is best treated with some mildly astringent and anodyne application. The following liniment is excellent for the purpose: Rx. Unguenti Stramonii oz. j; Liquoris Plumbi Subacetatis fl. drachm ss; Olei Lini fl. oz. iv.—M. fiat linimentum. As a rule, it is best to avoid poultices applied over the pock itself, for they soften the tender structures that make up its dome and render it prone to rupture, with all the consequences that may follow its conversion into an open sore. When the latter accident has occurred, dusting powders will ordinarily suffice to absorb the discharge, and thus prevent putrefaction—either the ordinary toilet powder or salicylized or carbolized powders, the basis of which may be starch with a small proportion of the oxide of zinc. Besides the antiseptics mentioned, iodoform, boric acid, etc. may be used to advantage. Liquid applications are not usually so appropriate, but the writer has known the proprietary preparation termed Listerine to answer admirably.

Circumscribed collections of pus are to be treated as under other circumstances, and burrowing is to be guarded against. It is only in the worst cases that constitutional treatment of any sort is demanded, and in these it should be of a supporting nature.

Passing from the simple inflammatory complications to those of a specific character, we will first mention erysipelas. Genuine erysipelas following vaccination is quite rare, but when it does occur it is prone to prove serious. The writer believes that it always depends on secondary infection—i.e. that the vaccinal wound becomes the nidus of an erysipelatous contagium already existing in the patient's surroundings, just as any other traumatic surface might, and that the vaccinal virus has nothing whatever to do with it. Admitting that improper virus is apt to give rise to dangerous inflammatory complications, the latter are not really erysipelatous, whatever guise they may put on. Erysipelas following vaccination calls for no other treatment than what is proper for traumatic erysipelas under ordinary circumstances.

We now come to the subject of vaccinal syphilis. The question of the possibility of conveying constitutional taints along with vaccinia was raised long ago, but, partly relying on certain theoretical tenets, and partly because of the rarity of well-ascertained facts to shake the blind confidence felt in the utter harmlessness of vaccination, the profession fought the suggestion without properly investigating it. In regard to syphilis, the broad assertion was maintained that two infectious diseases could not affect an individual at one and the same time: either syphilis would be communicated alone or vaccinia alone; moreover, it was affirmed that the juices of a syphilitic person were not capable of giving rise to the disease by inoculation unless they happened to proceed from a syphilitic lesion. There was never sufficient basis for the former of these two doctrines, and the latter received a rude shock when it was shown by Pallizzari and the anonymous physician of the Palatinate that the blood of a syphilitic subject was capable of conveying the taint. Meantime, certain horrible outbreaks of syphilis were reported, chiefly in Italy, that could not reasonably be imputed to the ordinary occasions of syphilitic infection. Even these occurrences, however, failed to shake the general incredulity, especially in Great Britain, where until quite recently men's orthodoxy in medical matters was gauged by their obstinacy in refusing to investigate, far less believe, the slightest proposition unfavorable to vaccination, and where, also, observations from beyond the limits of the empire were looked upon as in all probability fallacious.

To a Frenchman, M. Viennois, we are indebted for the first systematic and fair-minded study of the subject of vaccinal syphilis. This writer demonstrated that the Rivalta cases and those of other like outbreaks were certainly due to vaccination, but he concluded that they owed their occurrence not necessarily to the use of lymph from syphilitic subjects, but to the fact that that lymph contained blood. By this time it had come to be recognized that syphilis was inoculable by the blood. But even Viennois's masterly essay, and the facilis descensus it offered to those English authors who found themselves confronted with proof positive of their error, failed to make any noteworthy impression beyond the concession that syphilis might possibly be communicable in vaccination, but that, if it were, the catastrophe might easily be escaped by avoiding the use of lymph contaminated with blood, and that, therefore, the danger was practically no danger at all, for no one in England would think of using bloody lymph! In all this the English were slavishly followed by our own countrymen. It is proper to add, however, that Ballard of London did his best to present the matter in a proper light to the British profession, and that it is largely due to his labors and to those of Jonathan Hutchinson (the latter of whom supplemented Ricord's discovery that vaccine lymph is never free from blood with abundant clinical evidence of the existence of vaccinal syphilis unavoidable by the mere observance of Viennois's safeguard) that we are now freed from the clog of error in this matter. Nor was it the English alone that so long baffled the recognition of the truth; in the French Académie de Médicine, Jules Guérin and his adherents fought desperately against it.

At the present day we know that syphilis is liable to be communicated in vaccination, and that, too, without regard to visible blood in the lymph employed. There are two ways of avoiding it. One is, to use non-humanized lymph, since the lower animals are insusceptible to syphilis. This is simple. The other is, to select a human vaccinifer that is free from syphilis. This is difficult. Too great reliance, however, should not be placed upon the vaccinifer; it is possible to convey syphilis even in the use of bovine virus. Suppose two persons, A and B, are to be vaccinated at one sitting, A being syphilitic. If A is vaccinated first, and the same lancet, imperfectly cleansed, is used on B, it is plain that B will be inoculated not only with vaccine lymph, but also with A's blood. It is of the first importance, therefore, that this form of vaccinal inoculation of syphilis should be carefully guarded against; and that can be accomplished most certainly by using a fresh instrument for each patient.

Practically, this is certain, although there is some reason to believe that the disease may be conveyed to monkeys.

From a medico-legal point of view it is important to note that constitutional syphilis may follow vaccination, and yet have nothing to do with it. Suppose an infant to be born syphilitic, but with no visible manifestations of the taint. Let that child be vaccinated, and let the syphilitic dyscrasia afterward break forth. The ordinary inference would be that the syphilis was due to the vaccination; and in most instances this view would certainly be urged by the syphilitic parent, since it would free him from suspicion. It is always easy to disprove such an allegation, however, for syphilis communicated in vaccination always shows itself first in the form of a chancre at the site of the vaccination. Therefore in any given case, unless this mode of onset can be proved, the syphilis is manifestly not of vaccinal origin. Some observers, it is true, are of the opinion that vaccination may evoke a pre-existing syphilis, to use Lanoix's term—i.e. that it may hasten the appearance of the characteristic manifestations, and even determine their localization at the site of the vaccinal inoculation. But, even allowing the truth of that proposition, in such a case the lesion would be constitutional, not chancrous.

It is well, nevertheless, to take precautions against being placed on the defensive in this way; and it may commonly be avoided by declining to vaccinate infants under three or four months old, since inherited syphilis generally manifests itself by that time. This prudence on our own behalf should not be carried so far, however, as to lead us to deny the benefit of vaccination to very young infants whenever the prevalence of small-pox is such that they are in obvious danger of exposure.

As regards its management, vaccinal syphilis does not differ from the ordinary form of the affection, and hence demands no other treatment than what is proper for the disease contracted in the usual way. It simply originates in an extragenital chancre.

Concerning the conveyance of other constitutional taints in vaccination our knowledge is very limited. The present tendency of pathological investigation is, however, to accord inoculability to many diseases that formerly were not imagined to possess that quality, so that in regard to other affections than syphilis it is prudent to use the utmost care in the choice of lymph. There is one supposed safeguard that does not seem to have the slightest title to be so regarded—namely, the notion that a typical pock cannot be developed on a person affected with a specific cachexia. There is no truth in the doctrine. Over and over again the writer has seen perfect vaccine pocks on persons whom he knew to be syphilitic.

Cutaneous affections of a non-specific character are sometimes observed to result from vaccination; that is to say, they follow close upon its performance, without any other known exciting cause. It may fairly be supposed that in many instances they would have shown themselves even if the vaccination had not been performed, for it is often the case that we are unable to speak positively in regard to the exciting cause of an eruption. Several years ago a striking case in point was related to the writer by a well-known physician of this city, S. S. Purple, in whose practice it occurred. Purple had engaged to vaccinate a child on a certain day, but for some reason the vaccination was not done. In about a week from the appointed day, however, erysipelas made its appearance, beginning on the left arm at the usual site of vaccination, and pursued its course to a fatal termination. To be sure, we are now speaking of non-specific affections, but erysipelas illustrates the proposition perfectly, notwithstanding its specific character.

Children with a tendency to eczema are prone to suffer an outbreak of that disease as the result of vaccination. In Jenner's time, indeed, it was considered not only that there was great risk of causing an aggravation of any slight eczematous eruption by vaccination, but that the mere existence of the eczema, even in the most trivial form, was likely to interfere with the success of the vaccinal inoculation. This has been the general feeling of the profession. Quite recently, however, many observations have been recorded tending to show that the old dread of vaccinating an eczematous child was not altogether warranted. The question needs further study, and, while it is probably best to postpone the operation under ordinary circumstances, nothing should induce us to withhold its protective influence where there is any manifest danger of actual exposure to small-pox.

Although eczema is the most common of the cutaneous affections called forth or aggravated by vaccination, there are various forms of skin disease, some of them difficult to classify, that occasionally result. They are usually vesicular, pustular, or furuncular—that is to say, irritative. In the majority of instances it will be found either that the pock itself has followed an irregular course, being whitish, diffuse, and ending in an exaggerated although superficial incrustation, or that it has been subjected to injury. Still, in some cases neither of these conditions is the precursor of the skin affection. In many instances the latter can only be called nondescript. There seems to be some occult connection between vaccination and the curious skin disease described by the late Tilbury Fox of London under the name of impetigo contagiosa; and, indeed, Piffard of this city has found certain microphytes to be common to the crusting period of vaccinia and that of contagious impetigo. What the relation of the two affections is to each other, however, it is difficult to say.

Apart from impetigo contagiosa, the cutaneous complications that follow in the wake of vaccination possess no distinctive features, and their management differs in no wise from that of the same manifestations due to other causes.

THE TECHNICS OF VACCINATION.—This aspect of our theme involves a number of separate considerations. It will be convenient to give our attention first to the matter of the choice of virus. The question arises at once as to the selection between animal vaccine and the humanized variety. In a broad sense the term animal vaccine includes—1. Virus derived directly from a case of so-called spontaneous cow-pox. 2. Variola vaccine—i.e. the virus of an affection of the cow resulting from variolation. 3. The virus of horse-pox (not strictly vaccinal). 4. Retro-vaccine—i.e. the virus of an affection produced in the cow by the inoculation of vaccinia from the human subject. 5. The virus of a disease (true vaccinia) propagated through a series of bovine animals from the so-called spontaneous cow-pox, being the virus now commonly understood by the term, and the variety here referred to when it is not stated to the contrary.

By humanized vaccine we understand that which is obtained from the human subject, no matter how short or how long its descent from the cow. As regards animal vaccine, we may practically exclude from consideration all but the last variety mentioned, that being the one to which, in the great majority of instances, the term is now restricted. This narrows the question down to the choice between virus that has been propagated through a number of bovine animals (practically, calves) from the spontaneous disease in the cow, and that which, whatever its original source, has already passed through the human system.

The variety first mentioned, sometimes called primary vaccine, is generally spoken of by authors as not very trustworthy as regards its infective power (that is, not to be counted on to take), and as prone to give rise to undue inflammatory complications when its use does prove successful. These unpleasant qualities might be explained by the supposition that primary vaccine is not apt to be at its best when it is now and then obtained. Practically, however, it may be dismissed without further consideration, for it is seldom to be had.

The second form—variola-vaccine—is manifestly improper to be used whenever genuine vaccine is to be obtained, unless, indeed, we shut our eyes to the accumulating evidence that variola-vaccine, so called, is not vaccine at all. Furthermore, it is a question whether its use, as well as all attempts to produce it, should not be forbidden by law.

The third variety, if such it may be called, it does not seem legitimate to use in the present state of our knowledge, since it is not yet proved satisfactorily that horse-pox possesses the full protective power of cow-pox, or is free from objections that do not arise in connection with the latter.

As to retro-vaccine, while the writer is unable to see any positive reason against its use, neither can he see any reason why it should be superior to humanized vaccine, as such, save that during the period of its bovine propagation it is not liable to become contaminated with the poison of syphilis. The idea that an enfeebled stock of humanized vaccine can have new life infused into it by passing through the system of the cow is not reasonable primâ facie, and there are no particular facts to support it. By ensuring freedom from the danger of communicating syphilis retro-vaccination doubtless served a good purpose at one time, but now, since the remarkable and enduring excellence of the Beaugency stock is so well established, there seems to be no excuse for a further resort to the practice.

The last of our five forms of animal vaccine, that produced by the continued propagation of spontaneous cow-pox through calves, is what is now known as animal vaccine par excellence. Its advantages over the other forms are so obvious that it alone should figure in any comparison between animal and humanized vaccine. That being understood, what are the relative merits of animal and humanized vaccine? It should be stated, in the first place, that bovine virus should be compared with virus that has long been humanized, for lymph of but a few removes from the bovine animal does not show any noteworthy differences from animal vaccine itself.

In behalf of humanized virus it is maintained—1, that it is a more trustworthy preventive of small-pox; 2, that it is superior in its infective property, so that it is surer to take; 3, that it is more prompt in its action, thereby affording more speedy protection to persons who have actually been exposed to small-pox; 4, that its virulent property is easier of preservation, wherefore it is more to be depended on when it is necessary to keep it on hand for a long time or to transmit it to great distances; 5, that its use requires less skill, or, rather, less special knowledge of the peculiarities of the animal virus; 6, that it is less violent in its effects; 7, that it is less apt to give rise to irregular, and therefore more or less abortive and non-protective, forms of pock.

The first of these propositions, which asserts that humanized vaccine confers greater protection against small-pox than the animal virus, was warmly maintained by those who opposed animal vaccination on its first introduction into this country; but now the record of the past thirteen years, during which period bovine virus has more and more borne the brunt of the fight against small-pox, has disproved it in the judgment of all competent and fair-minded observers. So far, indeed, as the facts have been analyzed, they go to show that the reverse is the case—that bovine virus confers a more complete and a more lasting protection. Direct observation on this point is strengthened by the collateral fact that revaccination became at once astonishingly successful when the use of animal vaccine first gained currency, whereas now it is again declining in success; the explanation of which latter circumstance is, that it is now found difficult to revaccinate those whose primary vaccination was done with bovine virus—a striking indication of the permanence of the protection accomplished with the latter.

The second assertion—that humanized virus succeeds more readily than the bovine variety—is still maintained by many, but, it may confidently be said, by few if any whose experience with good animal vaccine has been large. The truth is, that every large public vaccination service in the country is now carried on almost solely with bovine virus, and that results are thus achieved that were not dreamed of in former times. Individual experience cannot weigh against this fact, but may be explained, rather, by what modicum of truth there may be in the fifth proposition, or by the assumption (surely a legitimate one, in view of the number of irresponsible and ignorant purveyors of animal vaccine that have thrust themselves before the profession since the advantages of the practice were established by the labors of others) that those whose observation leads them to a conclusion at variance with that reached by the great majority of trained observers have really been unfortunate in the quality of the virus with which they have been supplied. Whatever the explanation may be, however, there is nothing more certain than that the use of animal vaccine, properly carried out, is daily furnishing results that have never been excelled, if they have been equalled, in the employment of humanized virus on a like scale.

The third suggestion—that the humanized virus acts the more promptly of the two, and is therefore to be preferred for immediate protection—is plausible, since the areola (the alleged sign of systemic infection) forms somewhat later around a pock produced by animal virus than around one that is the result of vaccination with the humanized variety. The difference is one of a few hours only at the most, and it is not by any means a general occurrence; still, we may concede that in this respect the use of humanized virus is to be preferred under certain circumstances.

As to the fourth statement—that humanized virus is more tenacious of its infective property—strictly speaking, there is not a particle of truth in it. In the case of liquid lymph preserved in capillary tubes it has the semblance of truth, but, for reasons that will be more fully set forth hereafter, that is because it is difficult to get the virulent portion of bovine lymph out of the tube. In the form of dried lymph (the only form that ought to be used) animal vaccine may be sent to all parts of the world, and may be kept any reasonable length of time and without special care, without undergoing sensible deterioration, if tested by one who is familiar with its peculiarities and aware of the care that should be taken in using it. Under ordinary circumstances there is no difficulty about preserving animal vaccine with its energy practically unimpaired.

The statement that the use of humanized virus demands less special knowledge than that of bovine virus is conceded at once. That special knowledge is easily mastered, however, and no man fitted to practise medicine will look upon its acquirement as a bugbear or a hardship.

The impression, almost universal thirteen years ago, that humanized vaccine is less severe in its local and constitutional effects than the animal virus has been eradicated from the minds of all but those who still follow the teachings of the older writers rather than yield to what daily experience has been teaching during these thirteen years, or those who reason from exceptional cases rather than from a general drift. The truth seems to be this: with revaccinated adults animal vaccine acts somewhat more severely than the humanized virus; in infants, on the other hand, its action is not so violent as that of the humanized variety.

Concerning the seventh and last claim put forward in behalf of humanized vaccine—that it is less apt to give rise to irregular or spurious pocks—we may say that no form of irregularity has been observed by those who have lately used the bovine virus that was not well known to the older writers, who founded their observations wholly, or almost wholly, on the use of the humanized virus; nor is there any proof that such irregularities are more common now than formerly. The truth seems to be, that these irregular forms of pock seem to prevail at certain times, and not at other times, regardless of the particular stock of virus used, other things being equal. Why this should be so we do not know, but the fact is beyond dispute.

To sum up, then, we can only say that in barely one particular—that of promptness of action—can humanized virus justly be credited with any superiority, while in every other essential respect it is inferior, so far as any difference is to be observed.

What, on the other hand, are the points of superior excellence attaching to bovine virus? Setting aside certain extravagant assertions that have sometimes been made in its behalf, such as that it far exceeds the humanized virus in its protective virtue (which may be true, but is not yet proved), they may be put in general terms in the form of a denial of all the particular claims that we have enumerated as having been put forth for its rival. Such a denial, it has been seen, seems to the writer to be justified, save in the one particular that perhaps we should accord to humanized virus the merit of speedier action, and consequently greater certainty of protection, in cases of actual exposure to small-pox.

Besides these negative points in its favor, the foremost advantage of animal vaccine is the guarantee it gives that, properly used, no syphilitic contamination will result. On this point no argument is needed, for the cow is insusceptible to syphilis.

A second consideration in its favor is, that it can always be had in large quantities at short notice. The young practitioner of the present day can scarcely appreciate the importance of this fact, but whoever remembers the comparative helplessness in which, in past years, he has found himself in the face of a sudden outbreak of small-pox, not knowing which way to turn for an adequate supply of vaccine, will at once concede its force.

On the whole, then, it must be said that bovine virus is entitled to the preference as a rule, but that possibly it is well to resort to humanized lymph of early removes under the special circumstances above referred to. On no account should long-humanized vaccine be used so long as our present stocks of animal virus maintain the excellence they have thus far preserved, nor should humanized virus of any sort be preferred in the general run of cases.

Passing now to a consideration of the various forms of vaccine, disregarding its source, there are practically these three: the crust, liquid lymph preserved in capillary tubes, and dried lymph.

Until recently the crust, or scab, was much used in this country. Its capability of being preserved unimpaired for a long time was a valid excuse for this, especially in regions remote from the great channels of communication, and it was in such districts that the use of the crust was chiefly practised. That excuse scarcely exists now, for there are few physicians who cannot obtain a better form of vaccine within a very short time. The objections to the crust are two: 1. Most crusts are inert. Especially is this true of bovine crusts, which are wellnigh worthless. It must be confessed, however, that when once a crust has proved itself active it may be trusted to retain its infective property for a very long time. The writer has made successful use of crusts seven years old that had made the voyage to Japan and back; and they were bovine crusts too. Still, the rule is, that crusts are untrustworthy. 2. Their use is apt to be followed by undue inflammation, probably of septic origin, for they almost invariably contain putrescent or readily putrescible elements. It has even happened to the writer to cut open a crust that to all appearance was typical and innocent, and to find in its interior a cavity occupied by a pulpy, stinking slough. Manifestly, such material is unfit to be introduced into the system of any human being.

In regard to liquid lymph in tubes, it is not much used in this country, and its employment elsewhere is on the decline. At first thought, it would seem to be the best form of all, but experience does not bear out this view. In this form humanized lymph is vastly superior to animal lymph, but with every possible care in charging and sealing the tubes it is not uncommon to find their contents putrid. There are low vegetable organisms that are supposed to prey on the vaccinad. If there is any truth in this supposition, those organisms are certainly favored in their destructive luxuriance by keeping the lymph liquid, thus furnishing them with the best possible culture-fluid. Be this as it may, the fact is well ascertained that tube-lymph does not keep well. It has been mentioned already that bovine lymph stored in tubes is decidedly inferior to the same form of humanized lymph. This was long ago recognized by propagators of animal vaccine, but the cause remained a mystery until Warlomont of Brussels suggested that it was due to one of the physical peculiarities of animal lymph—that, namely, as already hinted at, by virtue of which its formed elements tend to attach themselves to any surface presented to them, leaving the supernatant liquid a mere inert compound of water, albumen, and salts; so that in the case of tube-lymph the virulent elements remain attached to the glass, and only the inert constituents are really used. This theory is exceedingly ingenious and plausible, but the writer is not aware that it has been proved. He does know, however, that in some South American countries, where calf lymph in tubes is used with success, the custom is to grind the tubes to powder, and inoculate with the resulting magma, glass and all. This practice is certainly not to be commended.

Dried lymph is the most efficient of all forms of vaccine, and, kept as it ought to be, it retains its infective power long enough to answer all ordinary requirements. The writer has used it three years old with success. It may commonly be counted on for six weeks. One fact should be borne in mind, however: the longer dried lymph has been kept the more care is necessary in its use, for by long keeping it becomes very hard, so that it is a work of patience to dissolve it off from the surface on which it was deposited. Failure to accomplish its solution is the most common cause of a lack of success in its employment.

The various forms of stored vaccine are esteemed by the writer in the following order: 1, dried bovine lymph; 2, dried humanized lymph; 3, humanized tube-lymph; 4, humanized crusts; 5, bovine tube-lymph; 6, bovine crusts.

The age and other circumstances under which it is best to vaccinate children constitute a point for practical consideration. It may first be mentioned that pre-natal vaccination has been advocated by some authors; that is to say, the vaccinal infection of the foetus in utero by vaccinating the mother during gestation. There seems to be respectable testimony going to show that the end may thus be accomplished, but a weighty objection arises in the fact that this mediate vaccination of the foetus produces no physical sign of its success, so that doubt must always be felt as to whether or not the procedure has been efficacious. Moreover, it is seldom indeed that a child needs protection before its birth, provided we protect the mother, for it is well known that vaccinia will overtake and destroy the variolous infection, even when the latter has had two or three days' start. The practice has been chiefly urged by Bollinger. It is not likely to come into general use.

There is no special objection to vaccinating an infant at any time after birth, but usually it is well to defer the operation until the child is about three months old, unless there is actual danger of exposure to small-pox. Yet it is not well to postpone vaccination until the period of dentition, for the combined irritation of the two disturbing elements may prove decidedly uncomfortable if not serious.

Something is to be said as to the time of the year to be chosen. In New York the bad custom prevails, especially among the poorer classes, of having children vaccinated only in April, May, or June—just the part of the year in which erysipelas is most rife. The hot months should not generally be chosen, for any source of irritation is apt to be felt more severely by infants during the summer heat. However, no circumstances should be looked upon as a positive bar to vaccination in case of actual danger of exposure to small-pox, and in large towns children should never be taken into public conveyances or carried into any promiscuous assemblage until they have been protected by vaccination.

The next question is as to the part of the body that should be selected for the inoculation. The region of the insertion of the left deltoid muscle is usually chosen—the left rather than the right, because most nurses habitually carry an infant on their own left arm, so that the child's left arm is uppermost, and hence less exposed to injury. The region of the deltoid insertion is comparatively free from the irritation of muscular contraction, and it is easily accessible. If two insertions are made, it is well to make one of them over the deltoid insertion and the other at a point about an inch distant on the line of the posterior border of the same muscle, for there the lymphatic connection with the axillary glands is less free, so that adenitis is not so much to be feared. To avoid a scar in a locality that may be exposed to view on certain occasions some mothers prefer that their daughters should be vaccinated on the lower limb. To this there is no special objection, further than that the lower limb is rather more exposed to rough handling than the arm. If the leg is chosen, the point of junction of the two heads of the gastrocnemius is an eligible situation.

The actual operation is performed in various ways. The old inoculators generally made an incision through the whole thickness of the skin, so that a pellet of subcutaneous fat rolled up into the little wound. This is wholly unnecessary; furthermore, it is objectionable, for it decidedly increases the risk of inflammatory complications. Still more to be avoided are the methods by inserting a seton imbued with the virus and by hypodermic injection or other like procedures. The best way is, simply to remove the horny layer of the cuticle, so as to expose the succulent portion of the epidermis. This surface is somewhat red, and from it a slight exudation of lymph will be observed, but there need not be the least flow of blood. By this procedure it is not uncommon to vaccinate a sleeping child without waking it. It is not only admissible, but preferable, not to wound the derma at all. Such an abrasion is easily made with an ordinary lancet, which, contrary to the advice sometimes given, should be very sharp; but no cutting or scratching should be done with it, only scraping with the convex part of its edge, precisely as in using an ink-eraser. Scratching instruments (such as the rake-like vaccinator often used or a row of needles set in a handle) are not easy to adapt to varying degrees of plumpness of the arm, and are apt to make too deep scratches, one at either side, while the skin between the two is scarcely touched. Whatever instrument is chosen, it should not be used again until it has been thoroughly cleansed—made chemically clean—which can be accomplished only by heating it or by wiping it off and then dipping it into a strong disinfectant solution.

Some individuals are refractory to vaccination, but complete insusceptibility is exceedingly rare. Various expedients have been resorted to in rebellious cases, such as vesication with ammonia-water, maceration of the skin for some hours with glycerine, and the like. The writer has known these devices to succeed, but he has not seen the slightest advantage in the plan recommended by Ceely, that of using a wound some hours old rather than one just made, although he has tried the experiment many times. It is not necessary to make a large abrasion; one as large as the little finger-nail is ample.

The next step is to apply the virus, and it should be so applied as to bring it into contact with every part of the denuded surface. In what is known as arm-to-arm vaccination, or its equivalent, calf-to-arm vaccination (by all means the most successful method, although not often practicable in this country), the liquid lymph, fresh from the vaccinifer's pock, is simply applied, when it will at once become diffused over the abraded surface without any special pains being taken to accomplish that end.

If dried lymph is used, particular care should be taken to see that it is actually dissolved and transferred from the substance on which it was dried to the abraded surface. Failure to accomplish this is the cause of almost all the lack of success that inexperienced vaccinators meet with. The lymph should be moistened with water, or, if it is quite old, with glycerine, before the abrasion is made, so that it may have time to dissolve. It should then be rubbed upon the abraded spot vigorously, and at least for the space of a full minute.

In the use of tube-lymph no other precautions are necessary than in arm-to-arm vaccination, but, simple as this method is, its results are unsatisfactory.

Crusts should be reduced to a powder, and then made into a thin paste with water or glycerine. A convenient way of powdering a crust is to rub it on a file or between two files. The paste is to be well rubbed upon the abrasion. The insertion of a solid piece of crust into a valvular incision is not to be recommended.

When the operation is finished it is well to keep the arm bare for about five minutes, but not necessarily until the spot has become dry. It is not well to apply any sort of plaster, but means should be taken to prevent the underclothing from sticking to the abrasion. For this purpose there is no objection to the shields that are furnished by the surgical instrument-makers. Usually, however, nothing of the sort is necessary.

THE STORAGE AND PRESERVATION OF VACCINE VIRUS.—Lymph should usually be taken on the eighth day, inclusive—never after the areola has formed. On the other hand, the writer's experience does not lead him to coincide with those who state that the earliest lymph that can be obtained is the most energetic. If it is to be dry-stored, the substance to be coated with it (slips of quill, ivory, wood, whalebone, glass, and the like) should be laid gently in the pool of lymph that exudes on puncturing the pock, and allowed to dry, preferably without the aid of artificial warmth. The layer of lymph should be plainly visible after it has dried. A second coating is advisable, as it serves to preserve the first.

Capillary glass tubes are either cylindrical or furnished with a bulbous expansion at the middle, the latter form being most commonly used. To charge a tube make sure that both ends are open, and then submerge one end in the pool of lymph. Capillary attraction will cause the tube to fill, and the process may be facilitated materially by inclining the tube toward a horizontal direction, so that the capillary attraction is not opposed by that of gravitation. Care should be taken to keep the applied end of the tube constantly submerged, or bubbles of air will enter it. The sealing may be done with a blowpipe, by simply holding the ends in a flame, or by means of sealing-wax or some similar substance. The satisfactory charging of tubes demands some practice, but a little patience will enable any intelligent person to succeed.

In regard to crusts, they should never be removed until the surface beneath has become cicatrized and they have been partially detached by the natural process. A crust torn off prematurely should never be used, and the same may be said of secondary crusts—i.e. those that form by the desiccation of the discharge from the raw surface left when the primary crust has been removed forcibly.

For the preservation of vaccine in these various forms tubes need only be kept in a cool place. Dried lymph and crusts should be guarded against dampness even more than against warmth. Their preservation may be decidedly favored by over-drying, either in an exhausted receiver or by keeping them in a closed vessel in the presence of sulphuric acid, chloride of calcium, or some other substance having a strong affinity for water. It is needless to say, however, that they should not come into actual contact with any such agent. While this artificial desiccation tends powerfully to preserve dried lymph, it makes it more difficult to use. When dried lymph or a crust is to be sent by mail or other conveyance, it should be wrapped in some impermeably envelope, for which purpose gutta-percha tissue is very convenient. Both these forms of virus should be kept in a cool place. There is no objection to keeping them on ice, provided they are well protected against moisture.

In conclusion, the writer wishes to say that the limited space at his command has compelled the assumption of a dogmatic rather than an inductive form in the construction of this article. To the reader who may wish to pursue the subject further—and it will well repay thorough study—he would recommend the following bibliography:

Ballard: On Vaccination: its Value and Alleged Dangers, London, 1868.

Bousquet: Nouveau traité de la vaccine et des éruptions varioleuses, Paris, 1848.

Bryce: Practical Observations on the Inoculation of Cow-pox, Edinburgh, 1809.

Ceely: Observations on the Variolæ Vaccinæ, Worcester, 1840.

Chauveau et al.: Vaccine et Variole, Paris, 1865.

Depaul: Nouvelles recherches sur la véritable origine du virus vaccin, Paris, 1863; De l'origine réelle du virus vaccin, Paris, 1864; et al.: De la syphilis vaccinale, Paris, 1865.

Hardaway: Essentials of Vaccination, Chicago, 1882.

Hering: Ueber Kuhpocken an Kühen, Stuttgart, 1839.

Jenner: An Inquiry, etc., 2d ed., London, 1800.

Sacco: Trattato di Vaccinazione, Milano, 1809.

Seaton: A Handbook of Vaccination, London, 1868.

Steinbrenner: Traité sur la vaccine, Paris, 1846.