Tuberculosis

Until the investigations and discoveries of the past few years, the presence of tubercles in the various organs and tissues of the body had been regarded as the essential element of tuberculosis. The evidence to be presented in the following pages will show that the immediate cause of tubercles may produce other lesions as well, and that the presence of a specific virus as the efficient cause of whatever may be the lesion, rather than the existence of tubercles, is to be regarded as the characteristic feature of the disease tuberculosis.

The tendency of the present is to regard the latter term as including the various morbid processes connected with the origin, presence, and growth of a specific, organized virus, their dissemination, metamorphoses, and effects. Whether all those processes in connection with which the virus is found are due to the latter, or whether some may not arise and exist independently of the same, are among the questions whose answer is remote rather than at hand.

As the presence of the cause of tuberculosis is the test demanded by some authorities for the existence of the process, so the anatomical classification has depended upon the existence of the tubercle. The substitution of tubercle for organized virus in the general definition of tuberculosis represents the distinction between the anatomical and the etiological classification of this affection.

A tubercle was originally a small rounded body, a little tuberosity, and at the close of the last century the specific tubercle was distinguished from other rounded nodules.

Till the discovery of Villemin, the recognition of the tubercle was essentially based upon its anatomical characteristics. Previous to the studies of Reinhardt and Virchow these related to appearances, which were attributed to a deposition of material, scrofulous or tuberculous, from the blood or lymph. The idea was eventually maintained that this material formed the basis of a growth or new formation, and Virchow showed that the tubercle was composed of a tissue, of cells and intercellular substance, growing within and from pre-existing tissues. He classified the tubercles among the tumors as circumscribed new formations whose structure resembled that of granulation-tissue. The specific tubercle was, at the outset, minute, smaller than a millet-seed, submiliary, although indefinite numbers of these minute tubercles might be grouped together and form closely massed aggregations. From this agglomeration of single tubercles, and their frequent association with inflammatory products, both of which were prone to early death and transformation into a cheese-like mass, the extensive tubercular infiltrations of organs arose. The latter were regarded as a frequent cause of the wasting disease phthisis, which was either pulmonary, intestinal, or renal according as the lungs, intestine and mesenteric glands, or kidneys were the predominant seat of the tubercular growth.

The histological features of the tubercle were further investigated by Wagner, who described the resemblances and differences of the structure of the tubercle and the lymphatic gland. Schüppel soon after published his monograph, essentially confirming the statements of Wagner. According to these observers, the typical tubercle, as found in lymphatic glands, presents essentially the same peculiarities of structure when seen elsewhere in the body. This structure consists of a non-vascularized network of fibres, in the meshes of which cells are imbedded. The fibrous network resembles the reticulum of a lymphatic gland, and nuclei are often found at those points where the fibres are united. This appearance has suggested that the network is formed of branching and anastomosing cells. Within the meshes are three sorts of cells—viz. giant-cells, epithelioid (endothelioid) cells, and small, round, indifferent cells. One or several giant-cells, each with its abundant nuclei, lie near the centre of the tubercle or are diffused throughout the same. These are usually immediately surrounded by the large epithelioid cells, with one or more nuclei, which are often so numerous as to compose the greater part of the tubercle. The indifferent cells, resembling lymph-corpuscles, occur singly or in groups, distributed throughout the tubercle more abundantly at the periphery, between the cells previously described, and with them completely fill the spaces of the fibrous network.

"Das tuberkelähnliche Lymphadenom," Archiv der Heilkunde, 1870, xi. 6; xii. 1.

Untersuchungen über Lymphdrüsen-Tuberkulose, 1871.

Although the typical tubercle is thus constituted, the structural features depend somewhat upon its age. It is generally admitted that the freshest tubercles, as found in the external coat of the smaller arteries of the pia mater, are composed of little else than a circumscribed accumulation of small, round cells, without a distinct reticulum. The giant-cells, the epithelioid cells, and the well-characterized reticulum appear as the tubercle increases in age. It is thought probable that the giant-cells represent the agglomeration of the small, round cells in pre-existing cavities, lymphatics, blood-vessels, or secretory canals. The epithelioid cells in like manner are considered to result from the enlargement or fusion of the smaller cells, while the reticulum represents either a secretion from, or a transformation of, the cellular elements of which the tubercle is composed.

The subsequent history of the tubercle is dependent upon its metamorphoses. These are known as cheesy degeneration, calcification, and fibrous transformation.

The absence of blood-vessels, already stated, and the abundantly cellular nature of the growth, with the possible action of micro-organisms, result in a tendency to the early death of the cells and a necrosis of the tubercle. This is the cheesy degeneration, and is regarded as a form of coagulative necrosis, which begins at the centre, advances toward the periphery, and results in the transformation of the gray into a yellow tubercle. This termination in cheesy degeneration likewise affects inflammatory products surrounding the tubercle, and even relatively normal tissues in which numerous tubercles may lie. This cheesy material either softens or becomes infiltrated with lime salts, calcified. The softening of the tubercle results in the formation of a material capable of removal as a discharge from the surfaces of the body or by absorption through the lymphatics and blood-vessels. In the former event ulcers arise upon, and cavities communicate with, the surfaces of the body opening externally.

The cheesy material frequently becomes calcified, thus remaining as a comparatively inert mass. The earthy salts may be diffused throughout a uniformly cheesy basis, or they may be deposited in a partially softened, cheesy menstruum, when a mortar-like material results.

The tubercle becomes fibrous with the diminution in the number of its cells and the increase in the thickness of the reticulum, with the transformation of the latter into a homogeneous hyaline substance. The cornified, horn-like tubercle is one whose size is diminished from the shrinkage of its cells into glistening flakes, without an evident associated cheesy or fatty degeneration.

The intimate relation of scrofula to tuberculosis has been variously expressed from time to time in accordance with the amount and accuracy of the existing knowledge. At the outset the enlargement of the lymphatic glands, especially of the neck, characterized the scrofulous affection. As the enlargements of the glands were found to present intrinsic differences connected with differing clinical histories, only those glands were regarded as scrofulous which presented the cheesy appearances. With the recognition of the cheesy condition of tubercles the latter were identified with the scrofulous gland, from the cheesy condition common to both.

This identification of scrofula and tubercle prevailed till Virchow showed that cheesy material might have a different origin, and maintained that there were cheesy lymphatic glands without tubercle, as well as tuberculous lymphatic glands which might become cheesy. A distinction was thus drawn between scrofula and tuberculosis. The former term was applied to that condition of the individual which favored the retention and cheesy degeneration of inflammatory products, not only in the lymphatic glands, but elsewhere in the body. Tuberculosis, on the contrary, was characterized by the production of tubercles which were often accompanied by retained inflammatory products, both of which were prone to undergo cheesy degeneration.

The frequent association of well-defined tubercles with what were regarded as antecedent scrofulous disturbances also suggested an intimacy of relation between scrofula and tuberculosis. Virchow had always maintained the possibility of regarding tuberculosis as a heteroplastic or metastatic scrofula. The occurrence of cases of tuberculosis without evidence of an antecedent scrofula prevented him from making a more absolute statement of the above relation.

Die Krankhaften Geschwülste, 1864-65, ii. 629.

The views with regard to the connection between scrofula and tuberculosis have become essentially modified of late years as a result of the investigations concerning the etiology of tuberculosis.

In 1856, Buhl first published his view, although he had for several years been impressed with the idea, that miliary tuberculosis was an infective disease resulting from the absorption of a specific virus. He based his theory upon the almost constant coexistence of one or several cheesy collections and miliary tubercles. The former were recognized as the remains of previous inflammatory processes, and the tubercles were looked upon as the immediate result of the absorption of this cheesy material. The individual thus infected himself. Buhl claimed that the simultaneous occurrence of tubercles and inflammatory products was the co-effect of the same cause, and that the acute miliary tuberculosis, as a localized process, was merely an inflammation with the development of tubercles. He restricted the term tuberculous inflammation, however, to those forms which necessarily and from the beginning, produced tubercles whose presence was limited to the tissue inflamed. The tuberculous inflammation was regarded as a primary condition, while the acute miliary tuberculosis was a secondary process resulting from infection.

Lungenentzündung, Tuberkulose und Schwindsucht, 1872, iii.

Op. cit., 123.

The tuberculous inflammation of this author was largely characterized by those features which, with the exception of the constant presence of tubercles, were recognized by others as attributes of a scrofulous inflammation. At the same time, he objected to the latter term as a substitute, since its use would imply that no other cheesy product than that from a tuberculous inflammation would serve as the origin of tubercles. Buhl strictly maintained that the absorption of any cheesy material, whatsoever its source, might give rise to a general growth of tubercle in the body.

The views of this author were popularized mainly through the teachings of Niemeyer concerning pulmonary consumption. The latter adhered to Virchow's views relating to scrofulous inflammation, but maintained that most consumptives were in imminent danger of becoming tuberculous in accordance with the doctrines of Buhl.

Klinische Vorträge über die Lungenschwindsucht, 1867.

The theory of an infectious origin of tuberculosis, advanced from time to time by others, but most forcibly presented and maintained by Buhl, was first demonstrated by Villemin in 1865. This observer showed that certain animals, especially rabbits and guinea-pigs, might be successfully inoculated, beneath the skin, with fragments of gray tubercle, cheesy products, sputum, and blood from cases of phthisis. The development of tubercles took place within three weeks after the inoculation, and became general within four weeks. He also demonstrated that rabbits became tuberculous when inoculated with bits of the tumors occurring in the pearly distemper of cattle.

Etudes sur la Tuberculose, Paris, 1868, 528.

Villemin's observations have been repeatedly confirmed and extended; although subjected to the severest criticism and control, their results are so constant that the law of the inoculability of tubercle is almost universally regarded as fixed. Its value as a test is evident from the statement of Cohnheim, who regards as tuberculous only that which produces tuberculosis when transferred to suitable animals. The transfer may be made in various ways. Chauveau and others were successful in producing an intestinal tuberculosis by the introduction of tuberculous material into the intestinal canal of animals, especially the Herbivora. Tappeiner succeeded in producing pulmonary tuberculosis, with or without general tuberculosis, in dogs, by compelling them to breathe air in which were contained minute particles of sputa from tuberculous pulmonary cavities.

Die Tuberkulose vom Standpunkte der Infections-Lehre, 1880, 13.

Virchow's Archiv, 1878, lxxiv. 393.

The production of a tuberculosis of the iris, as well as of remote organs, by the inoculation of tuberculous material into the anterior chamber of the eye, was an ingenious method devised by Cohnheim and Salomonsen. It permitted the direct observation of the several steps in the process of absorption of the inoculated material and development of the tubercles.

Cohnheim's Vorlesungen über Allgemeine Pathologie, 2te Auflage, 1882, i. 707.

The objections to the various experiments above alluded to are based upon the assumption that the results of the inoculation are not tubercles, but inflammatory products resembling tubercles. It is further advocated that the inoculation of indifferent material, as bits of glass or hairs, as well as other foreign substances, will produce the so-called artificial tuberculosis, especially in rabbits and guinea-pigs. It is admitted that these animals readily become tuberculous when exposed to simple inflammatory irritants, the local action of which frequently results in the production of cheesy material. This termination is now regarded as due to faults in the method of experimentation, the animals not being thoroughly protected from the influence of the virus of tuberculosis.

The objection on the ground of structure loses its force in connection with the well known differences in the structure of miliary tubercles in the human body, already mentioned. The tubercles resulting from inoculation often resemble in structure the meningeal tubercles of the brain rather than the type presented by tubercles in lymphatic glands. The development of tubercles in the iris may take place without any permanent inflammatory reaction. The association of evidences of inflammation with the development of the tubercle is therefore unnecessary.

The experiments of Villemin have not only demonstrated the infectious nature of tuberculosis, but have also led to a more accurate knowledge of the relation between tuberculosis and its allied affections, scrofula and pearly distemper.

The anatomical characteristics of scrofula have obviously proved insufficient in determining the relation presented by this affection to tuberculosis. The tendency to cheesy degeneration of its inflammatory products was the feature of chief importance. Villemin showed that portions of a scrofulous (cheesy) gland when inoculated were followed by tuberculosis, and that the inoculation of cheesy material from non-tuberculous or non-scrofulous sources was not followed by this result. The assumption of Buhl, that the absorption of cheesy material, as such, was the cause of tuberculosis, was thus disproved. The frequency with which the inoculation of cheesy material, from what were regarded as scrofulous sources, was followed by tuberculosis, led to more exact studies concerning the anatomical peculiarities of scrofulous inflammation. Köster called attention to the regularity of the occurrence of miliary tubercles in the fungous granulations of the inflamed joints of scrofulous and tuberculous individuals. Wagner and Schüppel discovered that scrofulous glands, in most if not in all instances, were tuberculous glands. The regularity of the presence of tubercles in scrofulous abscesses and ulcers of the skin and in scrofulous caries was shown by Friedländer. This observer likewise called attention to the presence of agglomerated tubercles as the chief constituent of the new formation of lupus. These anatomical discoveries resulted in uniting more closely the affections scrofula and tuberculosis from the histological standpoint, and the union has become more firmly cemented from the etiological investigations.

Virchow's Archiv, 1869, xlviii. 95.

Loc. cit.

Op. cit.

Volksmann's klinische Vorträge, 1873, lxiv.

Schüller has shown that the introduction of finely divided material from a scrofulous joint—that is, from one containing tubercles—into the lungs of rabbits was followed by a tuberculosis of the tracheal wound, the lungs, and liver. Similar experiments with reference to the introduction of lupus-tissue produced results suggestive of tubercle, if not actually tuberculous.

Untersuchungen über die Enstehung und Ursachen der Skrophulösen und Tuberkulösen Gelenkleiden, 1880.

The intimacy of relation between tuberculosis and pearly distemper is a necessary result of Villemin's experiment, in which the rabbit became tuberculous after inoculation with fragments of the pearly tumor. Gerlach, and especially Schüppel, showed that the structure of the nodules of the pearly distemper is the same as that of the tubercles of man, and that the two diseases are identical from the histological point of view.

Op. cit., 537.

Virchow's Archiv, 1870, li. 290.

Ibid., 1872, lvi. 38.

From the anatomical identification and the etiological connection, as shown by Villemin, Gerlach, and Aufrecht, the pearly distemper became designated as a bovine tuberculosis.

The experiments of Villemin were further productive in leading to the discovery by Koch of the bacillus tuberculosis. It was early obvious that certain cheesy material and gray tubercles possessed the infectious qualities, and Villemin maintained that the immediate cause of the latter was a germ introduced from without, which propagated and perpetuated itself in man and certain animals. This view acquired prominence through the investigations of Klebs, who in 1877 claimed to have isolated the micrococci which produced tubercles when injected into animals. Three years later Schüller confirmed the statements of Klebs, and asserted that he had been enabled to obtain infective micrococci by cultivation from miliary tubercles, scrofulous glands and joints, and from the tissue of lupus. Aufrecht found micrococci, single and in chains, and short glistening rods, within tubercles resulting from inoculation with material from pearly tumors. The same organisms were found in tubercles produced by the inoculation of tubercles from man, and he regarded these rod-shaped bodies as the specific element productive of miliary tuberculosis.

Op. cit., 620.

Op. cit., 55.

Pathologische Mittheilungen, 1881, p. 43.

The isolation of the virus of tubercle was thus regarded as an open question till the announcement by Koch of the constant presence of a hitherto unknown, characteristic, well defined organism in all tuberculous affections, which, when isolated and introduced into animals, produced tuberculosis, the resulting tubercles likewise containing the organism.

Berliner klinische Wochenschrift, 1882, p. 15.

The latter, the bacillus tuberculosis, was to be seen in preparations methodically treated and carefully stained with aniline colors, by all of which, excepting the browns, the bacillus was tinged. It was found in miliary tubercles of the lung, cerebral and intestinal tubercle, cheesy bronchitis and pneumonia, phthisical sputa, scrofulous glands, and fungous inflammation of the joints. It was also seen in the nodules of pearly distemper and in the cheesy masses from the lungs of cattle. It was furthermore met with in the cheesy lymphatic glands of swine, in the tubercular nodules of a fowl, and in the tubercles of guinea-pigs, rabbits, and monkeys. The bacilli were likewise found in the tubercles resulting from the inoculation of animals with tubercular virus from its various sources.

The microphytes were described as very slender rods, varying in length from one-fourth the diameter of a red blood-corpuscle to its entire diameter, and spores were occasionally seen within the rods. In shape and size they resembled the bacilli of leprosy, but the latter were narrower and pointed at the ends. They were found in greatest abundance when the tuberculous process was recent and rapidly advancing, and were present within, as well as between, cells. The younger giant-cells contained them in larger numbers than the older forms. They were present at the periphery of cheesy nodules rather than at the centre.

The bacilli were cultivated through successive generations and required a temperature of between 30° C. and 41° C. (86° F.-105.8° F.) for their development, one of 37° C. or 38° C. (98.6° F. or 100.4° F.) being the most favorable. The crop first became apparent on the tenth day after sowing, and the growth extended through a period of three to four weeks, forming a compact scale. The cultivated bacilli, even propagated through several generations, when inoculated, produced the same positive results as follow the inoculation of fragments of tuberculous material, although animals might be used which are not easily infected with tuberculosis.

Koch's publication was immediately followed by a statement from Baumgarten of his discovery of rod-like bacteria in the tubercles of rabbits resulting from the inoculation with pearly masses, and in the pleural and pericardial tubercles of man. They were made evident by treating the sections for microscopic examination with very dilute solutions of soda or potash.

Centralblatt für die med. Wissenschaften, 1882, xv. 257.

The discoveries of Koch thus show that the production of tuberculosis is dependent upon the presence of distinctive bacilli, and that these bacilli are present not only in miliary tubercles, but in scrofulous glands and joints, in cheesy inflammation of the lungs, and in the pearly distemper of animals. The identification of tuberculosis with the pearly distemper and certain scrofulous affections is thus established from the etiological as well as the histological point of view.

As the bacilli are to be regarded as the virus of tuberculosis, so their introduction into the human body is necessary for the production of this disease in man. It is obvious, however, that other factors than the virus are necessary, for not every one exposed to the reception of tubercular bacilli becomes tuberculous. It may well be that scrofula is still to be regarded as that condition of the solids and liquids of the body which offers favorable opportunities for the retention and growth of the bacilli, and thus for the production of tuberculosis. Formad claims that he has discovered structural peculiarities of tissue as a cause for the scrofulous habit, which he regards as synonymous with a predisposition to tuberculosis. These peculiarities are manifested by a narrowness of the lymph-spaces and their partial obliteration by cellular elements. He also maintains that these features are not only of congenital origin, but may be acquired through malnutrition and confinement.

Studies from the Pathological Lab. of the Univ. of Penna., reprint, 1882, xi. 3.

The occurrence of a local, circumscribed tuberculosis in extreme old age, without antecedent or other concurrent evidence of scrofulous disturbances, suggests that favorable opportunities for the development of the tubercular bacillus may arise in advancing years. In like manner, the frequent termination in phthisis of cases of diabetes suggests the likelihood of tuberculous inflammation arising in the absence of any evidence of previous scrofulous or tuberculous disease. The scrofulous condition or constitution, as indicated by vulnerable tissues, with a protracted course of inflammations, and a persistence of their products, with a tendency to cheesy degeneration, may still exist without a sign of tuberculosis. Those who claim that scrofula and tuberculosis are identical must, in the light of Koch's discovery, demonstrate the presence of the bacillus in all scrofulous inflammations, and deny the existence of scrofula apart from indisputable manifestations of the activity of the bacilli of tuberculosis. It may be that such evidence will be presented; until it is collected scrofula and tuberculosis are to be regarded as distinct though often coexistent. The scrofulous person is frequently tuberculous, the tuberculous person is usually scrofulous; the non-scrofulous person, however, may die of tuberculosis, while the individual may be scrofulous without containing tubercle.

The actual inheritance of tuberculosis is very unlikely, although this disease is frequently found in successive generations of a single family. The various members of the family are rather to be regarded as furnishing a suitable soil for the growth of the tubercular bacillus, and their exposure to its seed is favored by the existence of tuberculosis in one or more members of the household. The scrofulous condition is still to be regarded as hereditary as well as acquired, and the scrofulous remain as the class to be especially protected from the reception and effects of the bacilli of tuberculosis.

It is obviously a matter of importance to determine in any given case of phthisis whether bacilli are present or absent. A ready means of ascertaining this fact is offered by the examination of the sputum in cases of pulmonary phthisis, the feces in intestinal phthisis, the urine in renal phthisis, and the aspirated pus in cases of supposed tuberculosis of the joints. Koch has found in examining the sputa from numerous cases of phthisis that the bacilli were present in one-half the number, and that they were absent from the sputa of individuals who were not phthisical. Balmer and Fraentzel have found bacilli in the sputum from one hundred and twenty cases of phthisis, and concluded that the progress of a case of pulmonary tuberculosis might be readily determined from the number and degree of development of the typical bacilli present in the sputum. The more numerous and well-developed bacilli, with distinct and constant spores, were found in the graver cases, which advanced more rapidly. The sputum of the protracted cases contained few, small, and thin bacilli with scanty spores. The presence of fever was associated with numerous bacilli, while its absence was noted in those cases where but few were present.

Berliner klinische Wochenschrift, 1882, xlv. 679.

The bacilli are readily detected by means of the staining method devised by Koch. Various modifications have been presented from time to time, of which that of Ehrlich has proved the most satisfactory. The essential features are to obtain a dry, thin layer of a selected portion of the suspected sputum, which is then to be deeply stained with fuchsin or methyl-violet; the excess of color is to be removed with nitric acid, and the preparation is then ready for examination with the microscope. A power of four or five hundred diameters is sufficient for the recognition, and the object should be illuminated with a flood of light through a large diaphragm or an achromatic condenser. The bacillus retains the color notwithstanding its exposure to the acid, and the violet colors are more strongly presented if the preparation is tinted yellow after the action of the acid. If the bacilli are stained red with fuchsin, the background should be made blue. It is important that the reagents should be freshly prepared and filtered, that other bacteria may not obscure the picture, and that all the apparatus employed should be thoroughly clean.

Allg. med. Centr. Zeitung, 1882, xxxvii. 458.

A fragment of thick, opaque sputum is to be taken in forceps, placed on a cover-glass, and spread into a thin layer by means of a second cover-glass. The prepared slide is then to be passed slowly through an alcoholic flame, or that of a Bunsen burner, till the layer of sputum is dried. A saturated alcoholic solution of methyl-violet or fuchsin is made and filtered, and added, drop by drop, to a filtered, saturated solution of aniline oil shaken in water. The color is to be added with stirring till an opalescent film forms on the surface of the mixture. The slide containing the dried sputum is to be placed in or on this staining fluid, and allowed to remain for half an hour or less, the application of warmth hastening the process, when it is removed, and the specimen is decolorized in a solution of one part of nitric acid and two parts of water. The preparation is then washed in water, and may be examined directly in water, glycerin, or, after dehydration in alcohol, in oil of cloves. The tinted bacilli are made more prominent by a secondary staining, for a minute or two, of the red (fuchsin) preparation in a concentrated solution of methyl-blue, the violet preparation being secondarily stained in a like solution of aniline-brown. If the preparation is to be permanently preserved, it should be dehydrated in strong alcohol after washing with water, and it may then be treated with oil of cloves and mounted in Canada balsam.

After the observer has become thoroughly familiar with the tubercle bacilli by means of the method of Ehrlich, much time may be saved by following that of Baumgarten. The cover-glass bearing the dried sputum is placed in a very dilute solution of caustic potash (two drops of a 33 per cent. solution in a watch-glass of distilled water) till the layer of sputum becomes transparent. The cover is then placed on a slide moistened with a drop of water, tapped slightly, and examined with the microscope. The bacilli are readily seen, and may be differentiated from other varieties of bacteria, if necessary, by again drying the object and examining it in a drop of a dilute watery solution of aniline-violet or of other preparations of aniline used for staining nuclei. The tubercle bacilli remain unstained, while putrefactive bacteria are tinted.

Centralblatt für die med. Wissenschaften, 1882, xxv. 433.

The tubercular products of the invasion of the body by the bacillus tuberculosis are regarded as primary or secondary, according as they are present at that part of the body which directly receives the organisms or as they are dependent upon the transfer of the latter to parts remote from the region of their admission and immediate effects. This differing relation is also expressed by the terms local and general tuberculosis. In the former the bacilli excite the growth of tubercle only at a given part of the body. Their apparent effects may be wholly limited to this region, and it not rarely happens that the same is quite distant from the channels through which the bacilli are admitted. A general tuberculosis occurs when the latter are disseminated over the body, and their effects, especially the production of numerous tubercles, are found at various parts. The dissemination may take place at the time of entrance, or, as is more commonly the case, apparently occurs at some subsequent period, the immediate disturbances being localized at a given portion of the body. The necessary conditions being here offered for the propagation of the bacilli, their sudden distribution in great numbers is afterward permitted when favorable opportunities arise for their absorption. Such conditions are present when the local tubercular growths extend into lymphatics or blood-vessels. The frequency with which scrofulous glands are tuberculous—that is, contain miliary tubercles—is already fully recognized, and a tuberculosis of the lymphatic glands is essentially regional. These glands become affected in consequence of disturbances, the local effects of which may have wholly disappeared, in the region from which they receive their lymph. The cervical glands become permanently enlarged, perhaps tuberculous, in connection with persistent or recurrent inflammatory processes in the tonsils and pharynx, the bronchial glands from similar bronchial or pulmonary affections, and the mesenteric glands from like intestinal disturbances. In such instances, the direct reception of the bacilli into the lymph-current is assumed rather than demonstrated from a knowledge of the possibilities of absorption and an appreciation of the conditions in the glands.

That an actual growth of tubercles from the wall of the intestinal lymphatics may take place has long been known, and Ponfick has recently discovered that tubercles may be found growing from the wall of the thoracic duct. The possibility of the direct admission into the lymph-current of the infective element in tuberculosis is thus apparent, and its indirect entrance into the blood-current is equally obvious. That the bacillus of tubercle may be directly received into the blood-current is likewise evident from the observations of Weigert, who found tubercles growing from the walls of the pulmonary blood-vessels, venous as well as arterial. This discovery of a tuberculosis of the blood-vessels was confirmed by Klebs, who had found a tuberculosis of the azygos veins. The occurrence of multiple miliary tubercles of the pulmonary veins, especially near the place of entrance of smaller branches, has been asserted by Mügge, although appearances similar to those described by him may be met with, due simply to the agglomeration of white blood-corpuscles and their necrosis. Such a condition simulates very closely the miliary tubercle, but is usually analogous to the appearances figured by Virchow, and described by him as one of the phenomena of coagulation. In his observation the white bodies were adherent to the red clots, and were with them drawn from the pulmonary artery.

Virchow's Archiv, 1879, lxxvi. 243.

Die Cellular Pathologie, 4te Auflage, 1871, 184.

With the admission into the body, and the colonization of the tubercular bacilli, their effects may either be progressive until the death of the individual is occasioned, or, with the cessation of the growth of the bacilli or a possible modification of their noxious properties, recovery may ensue. The history of scrofulous glands, as well as that of circumscribed pulmonary inflammation in scrofulous persons, both presumably of a tuberculous nature, show that the effects of an invasion of the parasites may be overcome.

The regions of the body which are usually the seat of a primary tuberculosis are unquestionably the respiratory and intestinal tracts. With regard to the first of these regions, the one most frequently affected, there can be no doubt that in most instances the inhaled air carries the bacilli or their spores, or both. Their constant presence in the sputum of the frequent cases of tuberculous phthisis suggests a ready means for their escape into the atmosphere. The well recognized infective qualities of the sputum, as demonstrated by the various experiments before the bacillus was discovered, demand the thorough disinfection of phthisical sputa, since these are in all probability the chief source of the dissemination of the disease.

The tuberculosis of the intestine in like manner is to be regarded in the main as the result of an absorption from its surface of the specific agent. An obvious direct means of the approach of the bacilli is offered in the sputum, which, when swallowed, is likely to retain its virulent properties. The frequent coexistence of chronic pulmonary and intestinal tuberculosis is thus most readily explained. To what extent the presence of the bacilli in the pearly distemper of cattle and in the tuberculosis of other edible domesticated animals, as fowls and swine, may lead to an infection of the intestinal wall, still remains an unsolved problem. It is not yet determined at what temperatures the bacilli are destroyed, although their growth takes place only between 30° C. (86° F.) and 41° C. (105.8° F.). The inoculation of pearly masses produces tuberculosis in certain animals, yet the effect of cooking in destroying the bacilli and their spores is likely to prove of great importance. Aufrecht's attempts at inoculating rabbits with cooked pearly masses proved unsuccessful. Schottelius publishes an interesting series of observations relating to the prolonged use of meat from cattle affected with the pearly distemper, and shows that after a period of years no disease of the nature of tuberculosis occurred among the one hundred and thirty individuals included in the families concerned. Whatever may be the value of this negative testimony, there is, as yet, no evidence on the other side which satisfactorily determines the point in question—viz. that the flesh of animals affected with pearly distemper produces tuberculosis in the human consumer.

Op. cit., 51.

Virchow's Archiv, 1883, xci. 129.

The milk from cows thus diseased has likewise been regarded with suspicion, and the frequency of intestinal tuberculosis among children has been attributed to this source. Although the theoretical possibility of the escape of the bacilli into the milk of cows affected with pearly distemper is obvious, their presence in such milk is first to be demonstrated under conditions which necessitate their origin from the animal. If boiling the infective material for three minutes destroys its virulence, as claimed by Aufrecht, a ready means is offered of destroying the tubercle bacilli which may be present, not only in the milk from animals affected with pearly distemper, but in all milk which has been exposed for a certain time to an atmosphere which may contain the bacilli of tuberculosis. In the light of our present knowledge extreme hygienic precautions are only demanded in those cases where such a congenital or acquired basis (constitution) is present as facilitates the development of tuberculosis.