FERMENTATION. 281 



this disorder. 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 con- 

 stitute the contagium, because their infective power 

 was found to vanish in a few weeks. But other facts 

 established an intimate connection between the organ- 

 isms 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 re- 

 port, a young German physician, named Koch,* occu- 

 pied 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 hu- 

 mour of an ox's eye to be particularly suitable for their 

 nutrition. With a drop of the aqueous humour he 

 mixed the tiniest speck of a liquid containing the rods, 

 placed the drop under his microscope, warmed it suit- 

 ably, and observed the subsequent action. During the 

 first two hours hardly any change was noticeable; but 

 at the end of this time the rods began to lengthen, and 

 the action was so rapid that at the end of three or four 

 hours they attained from ten to twenty times their 

 original length. At the end of a few additional hours 

 they had formed filaments in many cases a hundred 

 times the length of the original rods. The same fila- 

 ment, in fact, was frequently observed to stretch 



* This, I believe, was the first reference to the researches of 

 Koch made in this country. 1879. 



