Ivii 



of the International Medical Congress in London, that Pasteur, 

 discussing his latest discoveries in the domain of immunity, paid a 

 graceful tribute to his great predecessor of nearly a century before 

 in this direction : " J'ai prete a l'expression de vaccination une 

 extension que la science, je l'espere, consacrera comme un hommage 

 au merite et aux immenses services rendus par un des plus grands 

 hommes de l'Angleterre, Jenner." From this time onwards 

 Pasteur's attention became concentrated upon the artificial production 

 of attenuated viruses or vaccines, and he set to work to prepare the 

 vaccine of anthrax. The simple method which had proved so 

 successful in the case of the fowl cholera virus had, however, to be 

 modified in that of anthrax, for the bacilli of anthrax, unlike those 

 of fowl cholera, possess the property of producing spores, so that in- 

 stead of exposure to the air diminishing the virulence of the culture, 

 it did but serve to afford the bacilli of anthrax an opportunity of 

 giving rise to spores, in which condition the virus is far more per- 

 sistent and far more hardy than in the bacillar form. 



It was necessary, therefore, to produce the anthrax vaccine by 

 preventing the production of spores and then ageing the cultivations 

 containing only the bacillar forms. This was accomplished by 

 keeping the cultures at 42 — 43° C, at which temperature no spores 

 are formed, and according to the length of time to which the cultures 

 are thus exposed more and more attenuated viruses or vaccines of 

 anthrax are obtained. 



The gain to France from the application of Pasteur's method of 

 vaccinating animals against anthrax has been estimated by M. 

 Chamberland at -5,000,000 francs in respect of the lives of sheep 

 which have been saved, and 2,000,000 francs for horned cattle. 

 Daring the ten years 1884 to 1894 it is stated that as many as 

 3,400,000 sheep had been vaccinated with a mortality of 1 per cent., 

 and 438,000 horned cattle, with a mortality of 3 per thousand. 



Pasteur also showed that whilst the bacillus of anthrax can be 

 rendered artificially less virulent, it can also become artificially en- 

 dowed by suitable treatment with an increased virulence. A dis- 

 covery which might at first sight appear to be of purely scientific 

 interest, but which has in due time been found to possess an 

 enormous practical importance. 



Graduated vaccines were also obtained of the microbe giving rise 

 to the disease known as Eouget de pore, or swine measles. 



And now we come to Pasteur's last and crowning achievement,, 

 the prevention of disease in man— his discovery of a cure for rabies 

 or hydrophobia. 



Here again the limits of space prevent our entering into the 

 details of this truly heroic struggle of the savant with the secrets of 

 nature. During five years, for Pasteur's researches on rabies were 



