SCIENCE IN MEDICINE 249 



count), he compares an equal part of blood with the bacterial 

 emulsion which is to be counted. These are mixed together 

 and a stained film is made. Then, by counting a large number 

 of red blood-corpuscles and the number of bacteria seen whilst 

 counting them, a comparison between the two is easily insti- 

 tuted. For instance, if 1,000 bacteria are seen whilst counting 

 500 red cells, the bacterial emulsion contains twice as many 

 bacteria as the blood does red blood-corpuscles. We will 

 suppose that the red blood-count proved to be normal — that is 

 to say, that the individual had 5,000,000 red cells in 1 c.mm. 

 of his blood — then the emulsion under investigation contains 

 10,000,000 bacteria per cm. In this way we can regulate our 

 doses of vaccine almost as accurately as we can our dose of 

 alkaloid or salt." l 



An alternative to counting the number of bacteria in a 

 vaccine is to weigh them. This method is used in the prepara- 

 tion of Koch's New Tuberculin (T. R.) The growth of tubercle 

 bacilli is suspended in alcohol and put into cylinders with a 

 number of porcelain marbles. The cylinders are rolled round 

 and round, and in this way the culture is broken up. The 

 alcohol is then allowed to evaporate, and there remains a 

 powder, which consists of crushed tubercle bacilli. This 

 powder is weighed, and 10 mgm. are suspended in 1 c.c. of salt 

 solution. 



(4) The Opsonic Index. — We must have the means of deter- 

 mining an appropriate dose. The discovery of Opsonins and 

 the method of estimating them quantitatively has given us a 

 means of doing this, a dose being good or bad according as it 

 increases the opsonins in the blood or no. 



The method of estimating the opsonic power of any given 

 blood consists in bringing together white blood-corpuscles, 

 bacteria suspended in salt solution, and the blood serum, and 

 allowing them to remain together for a certain time at the 

 temperature of the body. 



A solution containing 1*5 per cent, sodium citrate and '85 per 

 cent, sodium chloride is prepared and sterilised. The finger is 

 then pricked with a sterile needle and a bandage wound round 

 the finger above the punctures, so that the return of blood from 

 the distal portion of the finger is prevented. The blood is then 

 allowed to flow into a test tube containing the above solution. 



1 Treatment^ May, 1906. 



