ii4 Immunity 



diminished in virulence. He also found that when the organ- 

 isms had been so attenuated, they could not regain virulence 

 without artificial manipulation. It occurred to him that 

 such organisms, possessing feeble virulence, might be able 

 to confer immunity upon animals into which they were 

 inoculated, and he continued to investigate the subject until 

 he found that by using three " vaccines" or modified cultures 

 of increasing virulence, it was possible to render animals 

 immune against the unmodified organisms. This method 

 was put to practical test with great success, and has since 

 been extensively practised in different parts of the world. 



Arloing, Cornevin and Thomas,* and Kittf found that 

 exposure of the Bacillus anthracis symptomatici to a high 

 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. 

 By repeated inoculation of more and more active viruses 

 animals acquired complete immunity 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 incuba- 

 tion period of the disease. 



Haffkine found that the introduction of killed cultures 

 of virulent cholera spirilla produced immunity against the 

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



"Le Charbon Symptomatique du Boeuf," Paris, 1887. 

 t "Centralbl. f. Bakt.," etc., i, p. 684. 



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

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



