BACTERIAL VACCINES 283 



per cent NaCl). The number of bacteria per cc is deter- 

 mined by staining a slide made from a small volume of the 

 emulsion mixed with an equal volume of human blood drawn 

 from the finger and counting the relative number of bac- 

 teria and of red blood corpuscles. Since the corpuscles are 

 normally 5,000,000 per c.mm., a simple calculation gives 

 the number of bacteria. The emulsion of bacteria is then 

 diluted so that a certain number of millions shall be con- 

 tained in each cc, "standardized" as it is called, then heated 

 to the proper temperature for the necessary time and it 

 is ready for use. A preservative, as 0.5 per cent phenol, 

 tricresol, etc., is added unless the vaccine is to be used up at 

 once. The amounts of culture, salt solution, etc., vary with 

 the purpose for which the vaccine is to be used, from one 

 or two agar slant cultures and a few cc of solution, when a 

 single animal is to be treated, to bulk agar cultures and 

 liters of solution as in preparing antityphoid vaccine on a 

 large scale. 



Agar surface cultures are used so that there will be as 

 little admixture of foreign protein as possible (see Anaphyl- 

 axis, page 288 et seq.). Normal saline solution is isotonic 

 with the body cells and hence is employed as the vehicle. 



Lipovaccines.— The suspension of bacteria in neutral oil 

 was first used by Le Moignac and Pinoy, who gave the name 

 "lipovaccines" {Xctio::^ lipos = fat) to them. It was claimed 

 that the reaction following injection of these vaccines was 

 less severe than with saline vaccines in many instances; 

 also, that the bacteria were much more slowly absorbed. 

 For these two reasons it was hoped that much larger 

 numbers of bacteria could be injected at one dose and one 

 injection w^ould suffice instead of three or more as ordinarily 

 used. The technic of preparation, standardization and 

 killing of the organisms has not as yet been sufficiently 

 well established to warrant the general substitution of 

 lipovaccines for ordinary saline suspensions. 



Vaccines are either ''autogenous'' or "stock.'' An "autog- 

 enous" vaccine is a vaccine that is made from bacteria 

 derived from the individual or animal which it is desired to 

 vaccinate and contains not only the particular organism but 



