MLCROSCOPIC ORGANISMS IN INTESTINAL CANAL. 259 
basis in order to secure an abundant production of a fresh 
generation. This is of course merely the parallel of what we 
find occurring in regard to the Ozdium and bacteria of human 
excreta, where a solitary and excessive development of the organ- 
isms occurs, terminating in the production of innumerable re- 
productive elements incapable of germination until transferred 
toa fresh medium. In the case of cow dung, we certainly cannot 
ascribe the failure of excessive bacterial development to exhaus- 
tion by organisms of the same nature; but the variety and 
succession of other organisms which are developed may, perhaps, 
practically produce a similar result. 
While fresh cow dung is relatively deficient in bacteria, it is 
by no means devoid of distinct organisms generally. On the 
contrary, we find it almost invariably containing a very large 
number of zoosporoid bodies (Pl. XVIII, fig. 17), and some- 
times smaller numbers of other infusorial forms of various kinds. 
After prolonged study of the zoospores under various circum- 
stances, I am unable to indicate any coustant differences to 
distinguish them from those of human excreta. Like the latter, 
they exhibit numerous varieties in form and in character of 
movements, but none of these are peculiar to them. They seem 
also to be similarly affected by reagents artificially added to the 
basis, or by spontaneous changes taking place in it, and altogether 
there can, I believe, be no doubt of the identity of the organisms 
in both media. Although so constantly present, they may, like 
those of the human excreta, readily escape detection, unless 
suitable precautions are taken in preparing the specimens for 
examination. A dilution of the basis with pure water is fre- 
quently so rapidly fatal to them as almost entirely to conceal 
their presence, and even other solutions more favorable to them 
must be added with caution so as to avoid too abrupt a change 
of conditions. The best method of treating preparations, with 
a view to their detection, is to spread out a minute portion of 
the basis in a thin layer on a slide, then apply a cover glass, and 
(having first focussed a field containing a view of a portion of 
the margin of the layer) to introduce some strong solution of 
the same dung from which the specimen was procured, and 
which has been previously filtered, boiled, and allowed to cool. 
On doing this, the organisms may be observed emerging from 
the margin of the basis, and, after swimming actively in the 
fluid for a short time, gradually passing on into the series of 
changes described as occurring in those of human excreta under 
similar circumstances. Here, too, we find that those which, in 
place of emerging into the peripheral fluid, enter some of the 
interstitial spaces existing between the solids of the basis, retain 
their vitality much longer than their neighbours, 
