LOUIS PASTEUR. 247 



Following these experiments, or rather running con- 

 currently with some of them, came the experiments with 

 the microbes of fowl cholera which were destined to have 

 such a tremendous influence on the development of latter- 

 day medicine. In fowls suffering from fowl cholera there 

 had already been described extremely minute micro- 

 organisms which had been supposed by Moritz, by Peroncito, 

 and also by Toussaint to be the cause of the disease. 

 Pasteur isolated the organism in pure culture, grew it in 

 alkaline chicken broth, and then by introducing small 

 quantities of the broth culture (the one-hundredth or even 

 the one-thousandth part of a drop) under the skin re- 

 produced the disease in the fowl and the bird died. Pasteur 

 found that by making successive cultures at short intervals, 

 each new one from that made twenty-four hours before, the 

 virulence of the bacillus of fowl cholera remained unchanged. 

 If, however, a cultivation was kept for some time (three 

 months) protected from dust, but with free access of air, it no 

 longer retained its full virulence, and the birds inoculated with 

 small quantities, though they suffered some illness, did not 

 die. If, now, after they have passed through this mild attack 

 of the disease, they are inoculated with the non-attenuated 

 fowl cholera virus or cultivation — which before would un- 

 doubtedly have killed them — they may have a pretty smart 

 attack of illness, but the majority of them recover. This 

 was the first case in which an experimenter had been able 

 to modify a virus outside the body, and so obtain a protect- 

 ing virus or one capable of inducing a mild form of disease 

 which would protect against the attacks of a more active 

 virus. The difficulty of obtaining control over the 

 virulence of a disease was overcome when the modified 

 virus had been produced. Well may M. Valery-Radot quote 

 M. Bouley, who said when Pasteur announced his work to the 

 Academy of Sciences : " This is but the beginning. A new 

 doctrine opens itself in medicine, and this doctrine appears 

 to me powerful and luminous. A great future is preparing: 

 I wait for it with the confidence of a believer and with the 

 zeal of an enthusiast." 



It was but the beginning ; ere long Pasteur was able to 



