BACTERIAL VACCINES 175 



venient point with a wax pencil. Next an equal 

 amount of the bacterial suspension is drawn into 

 the tube, allowing a tiny air-bubble to intervene. 

 The two fluids are then expelled on a glass slide, 

 and thoroughly mixed by sucking back and forth 

 a number of times. After this has been done the 

 mixture is spread in the ordinary way of making 

 blood smears. If these blood smears, after stain- 

 ing, are examined with a microscope having a ruled 

 eye-piece, it is a simple matter to determine the 

 ratio of bacteria to blood cells. Taking the red 

 blood cells as 5,000 million per cc., one calculates 

 the number of bacteria per cc. In practice it is 

 advisable to so dilute the bacterial suspension that 

 the dose to be injected is contained in about one 

 cc. of fluid. Finally \ per cent, of carbolic acid 

 is added as a preservative. Such a suspension is a 

 " bacterial vaccine." It goes without saying that 

 the vaccines should be tested by means of cultures 

 to insure sterility, and that contaminations should 

 be excluded by means of microscopical exami- 

 nation. 



Doses. So far as doses are concerned, these vary 

 with different bacteria, and also according to the 

 indications, opsonic or clinical. The ordinary dose 

 for the staphylococcus vaccine is from 200,000,000 

 to 1,000,000,000 organisms; for the streptococcus 

 it is from 50 to 75 or 100,000,000, and for typhoid 

 from 750,000,000 to 1,000,000,000 bacteria. All 



