806 The American Naturalist. [September, 
tion. We cannot reduce the circumference of the animate 
world, however many radii and concentric circles we draw 
around our specialties. We may limit the province but not 
the realm. If we limit our study to man, we do not annihil- 
ate his relations to the rest of the animate world. Human 
physiology and human morphology represent only the latest 
terms of series stretching back to remote initial terms. The 
complexities of structure and function of the later terms we 
can never hope to understand until, through the study of a 
sufficient number of mean terms, we are able to determine 
the initial ones. 
Three general series, each more or less incomplete, are acces- 
sible to study: (1) The systematic series, consisting of adult 
organisms, (2) the paleontological series, and (3) the develop- 
mental series. Morphology approaches these series by com- 
parative study, and seeks to make each contribute as complete 
a story as possible. The same sources and the same method 
are open to physiology. The importance of the comparative 
method in physiology and the intimate co-relationship of 
physiology with morphology are well exemplified in a charm- 
ing little treatise by Metschnikoff on “ La Pathologie Comparée 
de l Inflammation ”—a work that must be reckoned as one of 
the fairest gems that adorn the annals of the Pasteur Institute. 
This monumental work shows how medicine itself must take 
its lessons from comparative biology, and approach its work 
from the standpoint of evolution. 
The history of morphology and physiology is one continu- 
ous illustration of their inter-dependence. When the famous 
Harvey was asked what led him to think of the circulation of 
the blood he at once referred the original suggestion to one of 
the morphological features of the vaseular apparatus—the 
valves and their arrangement. The hint furnished by struct- 
ure was then followed up and tested by experiment, and the 
result was a discovery that brought the position of valves, pul- 
sation of the heart, effects of ligatures, and other facts into 
rational relation to one another. 
The history of theories of generation furnishes a capital 
example of how physiological speculation has been guided, 
checked, and corrected by morphological discovery. The old 
