ANTIIKAX 259 



aration of the animals, and care in the disposal of the car- 

 r;i->s and in disinfection will do much to prevent continued 

 It has been shown that tin* loss of one or two animals 

 from a herd by anthrax- is a more common occurrence than 

 is ;i more extensive outbreak. Carelessness, however, may 

 result in great losses. 



Vaccination. The development of a protective treatment 

 against anthrax was one of the great gifts of Pasteur to the 

 world. Starting from observations he had made on chicken 

 cholera, he devised ways of attenuating the anthrax organ- 

 ism by growing it at a temperature above its optimum. 

 The longer the organism was grown at this unfavorable tem- 

 perature, the less virulent it became. The weakened 

 organism was unable to produce a serious form of the dis- 

 ease when introduced into the tissues of a susceptible ani- 

 mal. It did, however, grow, and cause the animal to 

 produce substances that protected it against a natural 

 attack of the disease. The original method of Pasteur was 

 to apply the vaccine in two doses at an interval of ten days. 

 The vaccines were standardized by injecting them into 

 small animals. The first vaccine should possess such a de- 

 gree of virulence that it would kill white mice, but not 

 guinea-pigs; the second should kill the latter animal, but 

 not rabbits. This mode of treatment caused the loss of 

 about 1 per cent, of the treated animals. It served to re- 

 duce the losses in cattle and sheep, especially in France, to 

 a marked extent. The immunity thus conferred is active in 

 form, persisting for about one year. 



It is evident that difficulties are encountered in the 

 preparation of the vaccine. If it is weakened too much, it 

 will give but a slight degree of protection. If, on the 

 other hand, it is not weakened sufficiently, the animals with 

 a low degree of resistance will be unable to withstand the 

 effects of the vaccine and will die. The vaccines also de-. 



