PER MENTA TlON. 555 



like to bring it home to your intelligence by a single trust- 

 worthy illustration. In 1850, two distinguished French 

 observers, MM. Davainne and Rayer, 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 Rayer. 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. Burdon 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 contagium, 

 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 investigation 

 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 tlie researches of Koch 

 made in this country. 1879. 



