Tables for Preparing Dilutions

(of Serum, Disinfectants or other substances.)

In estimating the agglutinin content or titre of a serum, testing disinfectants and for many other purposes, it becomes necessary to prepare a series of dilutions of the material under examination, and in order to avoid unnecessary expenditure of labour it is convenient to adhere to some definite scale of increment, such for example as the following:

From dilutions of 1:10 to 1:80 rise by increments of 5.

From dilutions of 1:80 to 1:200 rise by increments of 10.

From dilutions of 1:200 to 1:400 rise by increments of 25.

From dilutions of 1:400 to 1:500 rise by increments of 50.

From dilutions of 1:500 to 1:1000 rise by increments of 100.

From dilutions of 1: 1000 to 1:5000 rise by increments of 250.

From dilutions of 1: 5000 to 1:10,000 rise by increments of 1000.

From dilutions of 1:10,000 to 1:100,000 rise by increments of 5000.

From dilutions of 1:100,000 to 1:1,000,000 rise by increments of 100,000.

When dealing with a substance of unknown powers—and this is especially true with regard to agglutinating sera—it is customary to run a preliminary test, using a few widely separated dilutions such as may be obtained in the following manner:

First Dilution—I.

1 c.c. serum + 9 c.c. normal saline solution = 10 per cent. solution or 1: 10 dilution (of which 1 c.c. contains 0.1 c.c. of the original serum).

When dealing with fluids other than serum the diluent is usually distilled water; whilst if the original substance is a solid the instructions would read:

1 gram o.s. + 10 c.c. distilled water = 10 per cent. solution, etc.

Second Dilution—II.

1 c.c. first dilution + 9 c.c. normal saline solution = 1 per cent. solution or 1: 100 dilution.

Third Dilution—III.

1 c.c. second dilution + 9 c.c. normal saline solution = 1 per mille solution or 1: 1000 dilution.

Fourth Dilution—IV.

1 c.c. second dilution + 9 c.c. normal saline solution = 0.1 per mille solution or 1: 10,000 dilution.

The following tables showing the secondary dilutions that can readily be prepared from each of these four primary dilutions for use in the subsequent determination of the exact titre will probably be found of service by those who are not ready mathematicians.