494 BACTERINS, SERUMS — VACCINES — ANTITOXINS 



called this the " opsonic index." 'This is not used as much as for- 

 merly because its accuracy is not as great ' as believed by its dis- 

 coverers. 



The method of preparation of bacterins is simple. They are 

 usually made by growing the bacteria on slant agar for a suitable 

 period of time (24 — 72 hrs.) and washing off the growth with phys- 

 iological salt solution. This suspension is then sterilized by heating 

 at 55° — 60° C. for an hour, diluted so as to contain the proper num- 

 ber of bacteria per mil and a disinfectant added, usually 0.5 per cent, 

 carbolic acid or 0.2 per cent, trikresol. 



The method usually employed for counting the bacteria is one de- 

 vised by Wright. This consists of a comparison of the number of 

 bacteria in a certain quantity of blood. Another method is by the 

 use of the hsemaeytometer. 



There seems to be no fixed rule or method by which the exact dose 

 can be determined. The response to the initial dose cannot be known 

 in advance of the injection. After the first injection is made and the 

 effect noted, the dose may have to be increased or decreased accord- 

 ingly. The number of bacteria injected at one time varies from 10 

 million to 200 billion, the average being 500 million to 1 billion. 



In connection with bacterin therapy, several terms are used, the 

 exact meaning of which should be thoroughly understood. 



Autogenous bacterins (vaccines) are those made from the same 

 strain of the germ as that causing the disease. Cultures are made 

 from the sick animal and are incubated and bacterins made from 

 these. 



StocJc bacterins (vaccines) are made from cultures kept in the 

 laboratory. 



Polyvalent bacterins (vaccines) are those prepared from more 

 than one strain of some species of bacteria. 



Mixed bacterins (vaccines) contain more than one species of bac- 

 teria as B. coli, Ps. pyocyaneus, Mic. aureus, etc. It has sometimes 

 •been compared to the " shot gun " prescription. 



The number of bacterins used in the treatment of disease is very 

 large. The most common are strepto- and staphylo-bacterin ; B. coli, 

 pneumonia or influenza bacterin and mixed bacterin. Also a bacterin 

 for contagious abortion and dog distemper is on the market. 



The administration of bacterins for prophylaxis is in many cases 

 ■ attended with good results. This is especially true in the most excel- 

 lent results secured in typhoid immunization in man. The thera- 

 peutic action of these agents in certain cases of chronic suppuration is 

 undoubted. However, we agree with Eichhom, who states as fol- 

 lows : 



" There is a tendency at the present time to employ bacterins for 

 almost every infection. They are being prepared against most of the 

 pathogenic organisms producing disease, irrespective of whether they 



