FERMENTATION. 556 
like to bring it home to your intelligence by a single trust- 
worthy illustration. In 1850, two distinguished French 
observers, MM. Davainne and Bayer, noticed in the blood 
of animals which had died of the virulent disease called 
splenic fever, small microscopic organisms resembling 
transparent rods, but neither of them at that time attached 
any significance to the observation. In 1861, Pasteur 
published a memoir on the fermentation of butyric acid, 
wherein he described the organism which provoked it; and 
after reading this memoir it occurred to Davainne that 
splenic fever might be a case of fermentation set up within 
the animal body, by the organisms which had been observed 
by him and Raver. This idea has been placed beyond all 
doubt by subsequent research. 
Observations of the highest importance have also been 
made on splenic fever by Pollender and Brauell. Two 
years ago, Dr. Burden Sanderson gave us a very clear 
account of what was known up to that time of this dis- 
order. With regard to the permanence of the coutagium, 
it had been proved to hang for years about localities where 
it had once prevailed; and this seemed to show that the 
rod-like organisms could not constitute the contagium, 
because their infective power was found to vanish in a few 
weeks. But other facts established an intimate connection 
between the organisms and the disease, so that a review of 
all the facts caused Dr. Sanderson to conclude that the 
contagium existed in two distinct forms: the one " fugitive " 
and visible as transparent rods; the other permanent but 
" latent," and not yet brought within the grasp of the 
microscope. 
At the time that Dr. Sanderson was writing this report, 
a young German physician, named Koch,* occupied with 
the duties of his profession in an obscure country district, 
was already at work, applying, during his spare time, 
various original and ingenious devices to the inrestigation 
of splenic fever. He studied the habits of the rod-like 
organisms, and found the aqueous humor of an ox's eye to 
be particularly suitable for their nutrition. With a drop 
of the aqueous humor he mixed the tiniest speck of a 
liquid containing the rods, placed the drop under his 
* This, I believe, was the first reference to the researches of Koch 
made in this country. 1879. 
