4 
MICROSCOPIC ORGANISMS IN INTESTINAL CANAL. 285 
and again it has been observed that elements which in their 
natural medium were in an inactive and seemingly dying con- 
dition were rapidly roused to activity and multiplication under 
their influence. Leaving the chances of excessive or repeated 
introduction of extraneous reproductive elements entirely out of 
account, the rapidity with which multiplication by division may 
occur, under favorable circumstances, appears to be amply suffi- 
cient to account even for the excessive multitudes of zoospores 
present in certain specimens of choleraic excreta. As a matter 
of observation, it is undoubted that processes of division may 
recur at a rate of two per hour in the same zoospore, and a 
calculation of the numbers which may thus be developed under 
favorable circumstances, even within comparatively brief periods, 
renders it evident that the numbers of parasitic elements present, 
even where most excessive, do not necessitate the conclusion 
that the parent bodies originally introduced must have been very 
numerous. 
Experiments on the artificial introduction of the sporangia 
into the bodies of healthy animals have never been followed by 
any special result. I have again and again caused a dog to 
swallow large numbers of sporangia in all stages of develop- 
ment and desiccation without the treatment producing the 
slightest appreciable effect, and on one occasion introduced a 
solution crowded with spores into the peritoneal cavity of a 
guinea pig with as little result. The presence of morbid con- 
ditions certainly determines the degree of development of the 
parasite, but the presence of the latter seems to be incapable of 
giving rise to disease. The result of these experiments is sug- 
gestive, inasmuch as it shows how closely parasitic organisms may 
be associated with disease without being causally related to it. 
In many cases in which experiments have been supposed to 
demonstrate the essential dependence of disease on parasitic 
organisms, the procedure has not, as in the present case, con- 
sisted in the introduction of these organisms per se, but in the 
introduction of morbid fluids or other materials containing them. 
For example, we find Lésch affirming the essential causation of 
certain dysenteric conditions to lie in the presence of his Amada 
coli, beeause in one instance where he injected dysenteric excreta 
containing the parasite into the rectum of a dog, dysenteric 
lesions and a development of the parasite ensued. Now, there 
can be doubt that if in the present series of experiments morbid 
fluids containing the parasite had been employed in place of 
clean specimens of sporangia and spores, the results might have 
been very different. If a solution of choleraic or normal ex- 
creta containing the parasite had been substituted for the solution 
of the spores per se, in the experiment on the guinea pig, it may 
