556 FRAGMENTS OP RCtENCti. 
microscope, warmed it suitably, and observed the subse- 
quent 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 filament, 
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 graceful figures; while 
sometimes they formed knots of such bewildering com- 
plexity that it was impossible for the eye to trace the 
individual filaments through the confusion. 
Had the observation ended here an interesting scientific 
fact would have been added to our previous store, but the 
addition would have been of little practical value. Koch, 
however, continued to watch the filaments, and after a 
time noticed little dots appearing within them. . These 
dots became more and more distinct, until finally the 
whole length of the organism was studded with minute 
ovoid bodies, which lay within the outer integument like 
peas within their shell. By and by the integument fell to 
pieces, the place of the organisms being taken by a long 
row of seeds or spores. These observations, which were 
confirmed in all respects by the celebrated naturalist, Colm 
of Breslau, are of the highest importance. They clear up 
the existing perplexity regarding the latent and visible 
contagia of splenic fever; for in the most conclusive 
manner Koch proved the spores, as distinguished from 
the rods, to constitute the contagium of the fever in its 
most deadly and persistent form. 
How did he reach this important result? Mark the 
answer. There was but one way open to him to test the 
activity of the contagium, and that~ was the inoculation 
with it of living animals. He operated upon guinea-pigs 
and rabbits, but the vast majority of his experiments were 
made upon mice. Inoculating them with the fresh blood 
of an animal suffering from splenic fever, they invariably 
died of the same disease within twenty or thirty hours 
after inoculation. He then sought to determine how the 
contagium maintained its vitality. Drying the infectious 
