' ADDRESS. 17 
the great progress effected by the new method. It was soon introduced 
into his own institute and other laboratories throughout the world ; and 
it has immensely facilitated bacteriological study. 
One fruit of it in Koch’s own hands was the discovery of the microbe 
of cholera in India, whither he went to study the disease. This organism 
was termed by Koch from its curved form the ‘comma bacillus,’ and by 
the French the cholera vibrio. Great doubts were for a long time felt 
regarding this discovery. Several other kinds of bacteria were found of 
the same shape, some of them producing very similar appearances in cul- 
ture media. But bacteriologists are now universally agreed that, although 
various other conditions are necessary to the production of an attack of 
cholera besides the mere presence of the vibrio, yet it is the essential 
materies morbi ; and it is by the aid of the diagnosis which its presence in 
any case of true cholera enables the bacteriologist to make, that threatened 
invasions of this awful disease have of late years been so successfully 
repelled from our shores. If bacteriology had done nothing more for us 
than this, it might well have earned our gratitude. 
I have next to invite your attention to some earlier work of Pasteur. 
There is a disease known in France under the name of choléra 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 out- 
side the body for a protracted period under certain conditions, it under- 
went 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 culti- 
vated in the ordinary way. Thus was discovered the great fact of what 
Pasteur termed the atténwation 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 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 produeed by its attenuated virus and the protection afforded 
against small-pox by vaccination. And while pathologists still hesitated, 
1896. c 
