96 Immunity 



study phenomena of this kind, he investigated and found that when 

 chickens were inoculated with old and non-virulent cultures they 

 acquired immunity against virulent cultures. This led him to the 

 recommendation of the employment of attenuated cultures as 

 vaccines against the disease, and to the achievement of great success 

 in preventing epidemics by which great numbers of the barnyard 

 fowls of France were being destroyed. 



In 1 88 1 Pasteur,* in experimenting with Bacillus anthracis, ob- 

 served that if the organism were cultivated at unusually high tem- 

 peratures it lost the power of producing spores, and diminished in 

 virulence. He also found that when the organisms had been so 

 attenuated, they could not regain virulence without artificial manipu- 

 lation. 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, f and KittJ 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 85C. 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 calcium 

 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 followed 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 immuniza- 

 tion with the modified germs of the disease during the long incubation 

 period of the disease. 



* "Compte rendu de la Soc. de Biol. de Paris," 1881, xcn, pp. 662-665. 

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

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

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



