Immunity Acquired by Intoxication 95 



temperature in the dry state modified its virulence and 

 devised a practical method of protecting cattle against 

 symptomatic anthrax by inoculating them with powdered 

 muscle tissue containing the bacilli attenuated by drying 

 and exposure to 85 C. This method has since been in use 

 in many countries, and has given excellent satisfaction. 



In 1889 Pasteur,* continuing his researches upon the 

 experimental modification of the germs of disease and their 

 use as prophylactics, published his famous work upon rabies, 

 and showed that, although the micro-organism of that 

 disease had so far eluded discovery, it was contained in the 

 central nervous system of diseased animals, where it could 

 be modified in virulence by drying. By placing spinal cords 

 removed from rabid rabbits in a glass jar containing cal- 

 cium chlorid, he was able to diminish the virulence of the 

 contained micro-organisms according to the duration of the 

 exposure. The introduction of the attenuated virus was fol- 

 lowed by the development of a certain degree of immunity, 

 and was then followed by a more active virus, until by 

 repeated treatments the animals acquired complete immu- 

 nity against street virus. These experiments formed the basis 

 of the " Pasteur method " of treating rabies, which is nothing 

 more than immunization with the modified germs of the 

 disease during the long incubation period of the disease. 



Haffkinef found that the introduction of killed cultures 

 of virulent cholera spirilla produced immunity against the 

 living micro-organisms, and used the method with consider- 

 able success for preventing the disease. LaterJ he applied 

 the same method, also with considerable success, for the 

 prevention of bubonic plague. 



Wright followed pretty much the same method for the 

 prevention of typhoid fever. 



In all these cases the immunity induced by the experimen- 

 tal manipulations is specific in nature, and variable in inten- 

 sity, according to the method of treatment adopted and the 

 thoroughness with which it is carried out. This variability in 

 the results attained will be much better understood after the 

 subject of immunization against toxins has been discussed. 



2. Immunity Acquired by Intoxication. Bacterio-toxins 

 form a miscellaneous group of active bodies of entirely dif- 



* " Compte rendu de la Soc. de Biol. de Paris," 1881, cvm, p. 1228. 



t " Brit. Med. Jour," 1891, n, p. 1278. 



t Ibid., 1895, n, p. 1541. Ibid., Jan. 30, 1897, p. 256. 



