504 ON THE INTERDEPENDENCE OF SCIENCE 



I have next to invite your attention to some earlier work of Pasteur. There 

 is a disease known in France under the name of cholera des poules, which often 

 produced great havoc among the poultry yards of Paris. It had been observed 

 that the blood of birds that had died of this disease was peopled by a multitude 

 of minute bacteria, not very dissimilar in form and size to the microbe of the 

 lactic ferment to which I have before referred. And Pasteur found that, if this 

 bacterium was cultivated outside the body for a protracted period under certain 

 conditions, it underwent a remarkable diminution of its virulence ; so that, if 

 inoculated into a healthy fowl, it no longer caused the death of the bird, as it 

 would have done in its original condition, but produced a milder form of the 

 disease which was not fatal. And this altered character of the microbe, caused 

 by certain conditions, was found to persist in successive generations cultivated 

 in the ordinary way. Thus was discovered the great fact of what Pasteur termed 

 the attenuation des virus, which at once gave the clue to understanding what 

 had before been quite mysterious, the difference in virulence of the same disease 

 in different epidemics. 



But he made the further very important observation that a bird which had 

 gone through the mild form of the complaint had acquired immunity against it I 



in its most virulent condition. Pasteur afterwards succeeded in obtaining 

 mitigated varieties of microbes for some other diseases ; and he applied with | 



great success the principle which he had discovered in fowl-cholera for protecting 

 the larger domestic animals against the plague of anthrax. The preparations 

 used for such preventive inoculations he termed ' vaccins ' in honour of our 

 great countryman, Edward Jenner. For Pasteur at once saw the analogy between 

 the immunity to fowl-cholera produced by its attenuated virus and the protection 

 afforded against small-pox by vaccination. And while pathologists still hesi- 

 tated, he had no doubt of the correctness of Jenner's expression variolae vaccinae, 

 or small-pox in the cow. 



It is just a hundred years since Jenner made the crucial experiment of 

 inoculating with small-pox a boy whom he had previously vaccinated, the result 

 being, as he anticipated, that the boy was quite unaffected. It may be remarked 

 that this was a perfectly legitimate experiment, involving no danger to the 

 subject of it. Inoculation was at that time the established practice ; and if 

 vaccination should prove nugatory, the inoculation would be only what would 

 have been otherwise called for ; while it would be perfectly harmless if the 

 hoped-for effect of vaccination had been produced. 



We are a practical people, not much addicted to personal commemorations, 

 although our nation did indeed celebrate with fitting splendour the jubilee of 

 the reign of our beloved Queen ; and at the invitation of Glasgow the scientific 



