468 ANIMAL PHYSIOLOGY. 
of food, taken at one meal, that would otherwise lead to the 
above-noted attempts at its removal? Itis a mistake to ex- 
plain the result with reference to the alimentary tract alone. 
The entire metabolism of the body has a voice in the matter. 
From this point of view, the benefit of abstinence from spe- 
cific articles of diet, partial or complete, of taking at times 
very light meals, and much more that experience warrants, 
receives an explanation. Too little attention seems to have 
been given to this aspect of the subject that we are now en- 
deavoring to present briefly. 
Until the nature of metabolism is more completely under- 
stood, it will be impossible to treat the subject of diet, either 
in health or disease, with such confidence as to enable us to 
prescribe upon scientific principles alone. Very much must 
still be empirical, the outcome of trial and result, which is, 
however, after all, experiment in acrude form; and individual 
peculiarities that are inscrutable in their nature will always be 
encountered. Notwithstanding, if physicians will avail them- 
selves of the best that is known in the realm of physiologi- 
cal dietetics, and then contribute the results of their observa- 
tions in accurate form, substantial progress will be made in 
due time. 
Evolution— We have already alluded to some of those modi- 
fications in the form of the digestive organs that indicate an 
unexpected plasticity, and impress the fact of the close rela- 
tion of form and function. The conversion of a sea-gull into a 
graminivorous bird, with a corresponding alteration in the na- 
ture of the form of the stomach (it becoming a gizzard), with 
doubtless modifications in the digestive processes, when. re- 
garded more closely, implies coadaptations of a very varied 
kind. These are as yet but imperfectly known or understood, 
and the subject isa wide and inviting field for the physiolo- 
gist. Darwin and others have indicated, though but imper- 
fectly, some of the changes that are to be regarded in animals 
as correlations ; but in physiology the subject has received but 
little attention as yet. We have in several parts of this work 
called attention to it; but the limits of space prevent us doing 
little more than attempting to widen the student’s field of 
vision by introducing such considerations. The influence of 
climate on metabolism, an undoubted fact, has many implica- 
tions. 
Any one who keeps a few wild animals in confinement un- 
der close observation, and endeavors to ascertain how their 
