DIGESTION OF FOOD. 353 
tion of the gross conceptions of physical processes instead of 
the subtle though.at present rather indefinite ideas of vital 
processes. We prefer ignorance to narrow, artificial, and erro- 
neous views. 
Pathological—Under certain circumstances, of which one is 
obstruction to the venous circulation or the lymphatics, fluid 
may be poured out or effused into the neighboring tissues or the 
serous cavities. This isof very variable composition, but always 
contains enough salts and proteids to remind one of the blood. 
Such fluids are often spoken of as “lymph,” though the 
resemblance to normal tissue-lymph is but of the crudest kind; 
and the condition of the vessels when it is secreted, if such a 
term is here appropriate,.is not to be compared to the natural 
separation of the normal lymph—in fact, were this not so, it 
would be like the latter, which it is not. When such effusions 
take place they are in themselves evidence of altered (and not 
merely increased) function. . 
The Feces.—The feces may be regarded in at least a three- 
fold aspect. They contain undigested and indigestible rem- 
nants, the ferments and certain decomposition products of the 
digestive fluids, and true excretory matters. 
In carnivorous and omnivorous animals, including man, 
the undigested materials are those that have escaped the action 
of the secretions—such as starch and fats—together with those 
substances that the digestive juices are powerless to attack, 
as horny matter, hairs, elastic tissue, etc. 
In vegetable feeders a larger proportion of chlorophy], cel- 
lulose, and starch will, of course, be found. 
These, naturally, are variable with the individual, the spe- 
cies, and the vigor of the digestive organs at the time. 
Besides the above, certain products are to be detected in the 
feeces plainly traceable to the digestive fluids, and showing 
that they have undergone chemical decomposition in the ali- 
mentary tract, such as cholalic acid, altered coloring-matters 
like urobilin, derivable probably from bilirubin; also choles- 
terine, fatty acids, insoluble soaps (calcium, magnesium), to- 
gether with ferments, having the properties of pepsin and 
amylopsin. Mucus is also abundant in the feces. 
We know little of the excretory products proper, as they 
probably normally exist in small quantity, and it is not impos- 
sible that some of the products of the decomposition of the 
digestive juices may be reabsorbed and worked over or excreted 
by the kidneys, etc. 
28 
