FERMENTATION. 283 



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 

 6 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, 1 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 in- 

 vestigation of splenic fever. He studied the habits of 

 the rod-like organisms, and found the aqueous humour 

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

 tion. 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 suitably, 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 through 

 several fields of the microscope. Sometimes they lay 

 in straight lines parallel to each other, in other cases 

 they were bent, twisted, and coiled into the most grace- 

 ful figures ; while sometimes they formed knots of such 



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

 Koch made in this country. 1879. 



