BACTERINS 493 



cine as used by the Bureau of Animal Industry is as follows : Pro- 

 longed exposure to a high temperature serves to attenuate the viru- 

 lence of either fresh or dried virus. The material used for the vac- 

 cine is obtained from fresh black leg tissue (which contains B. chau- 

 veaui, the cause of the disease) by pounding the muscle tissue in a 

 mortar with the addition of a little water and squeezing the pulp 

 through a piece of linen cloth. The juice is spread in layers on plates 

 and is dried quickly at a temperature of about 35° C. This tem- 

 perature does not in the least affect the germs and the dried virus 

 obtained in this way retains a high degree of virulence for two years 

 or more. 



When vaccine is to be prepared, the dry material is pulverized 

 and mixed in a mortar with two parts of water, until it forms a semi- 

 fluid homogeneous mass. This is spread in a thin layer on a saucer 

 or glass dish and placed in an oven, the temperature of which can be 

 regulated and kept from 90° to 94° C. It should remain at this 

 temperature seven hours. When removed, it appears as a brownish 

 scale, which is easily detached from the disb. The scale is pulverised 

 and put up into packages of 10 doses each. Before it is used, it is 

 mixed with 10 mils water, filtered and the filtrate injected in doses 

 of 1 mil. 



An agent which is termed Black Leg Aggressin is also used for 

 immunization against this disease. It is prepared by first chopping 

 up fine black leg muscle. This is then frozen solid for several weeks, 

 then thawed out and the juice pressed out. This liquid is then passed 

 through a Berkfeld filter. It is administered subeutaneously. 



BACTERINS 



Among the first to employ " heat sterilized " virus for the pro- 

 duction of immunity in animals, was the " Father of veterinary medi- 

 cine in America," Dr. James Law, who in 1880 reported to the U. S. 

 Commissioner of Agriculture that he had been able to immunize pigs 

 to " swine fever " by this agent. He, in time, was followed by 

 Salmon, who immunized pigeons against B. suipestifer. Later 

 Moore obtained similar results in guinea pigs with dead bacteria, and 

 these were reported to the Washington Biological Society in 1893. 

 In 1894 Smith and Moore published the results of several series of 

 inoculations with heated cultures of hog cholera and swine plague bac- 

 teria. It was not, however, until 1903, due to the work of Wright 

 and Douglass, that this phase of Bacteriology received the impetus 

 which today places it in first rank in therapeutic and prophylactic 

 medicine. According to the work of these men, immunity is pro- 

 duced through the agency of opsonins, which increase the phagocy- 

 tosis. They also devised a method for estimating the power of the 

 blood serum to prepare bacteria for ingestion by the phagocytes and 



