As a result of all these means and methods of study, and as a part of
the great educational and scientific movement of the century, medical
men now take a wholly different view of the normal and abnormal
structures of the human body. The study of embryology has shown us that
many of the deviations from the normal development of the human body
are easily explained by embryology. One of the most important changes
in our idea, for example, of tumors is due to the fact that the study
of embryology and of the tissues of the embryo have shown us that
diseased structures, which lack explanation entirely, when compared
with the adult human tissues, readily find their explanation and fall
into an unexpected order when compared with the tissues of the embryo.
Not only, however, has the study of embryological tissues thrown a
flood of light on diseased structures, but we have obtained new views
of the relation of man to all creatures, lower in the scale of life.
Largely owing to the doctrine of evolution, we now recognize the fact
that, so far as his body is concerned, man is kindred to the brutes;
that his diseases, within certain limitations, are identical with
similar diseases of the lower animals; that his anatomy and physiology
are, in essence, the same as the anatomy and physiology of the lower
animals, even the very lowest, and that many of his diseases can be
best studied in the lower animals, because upon them we can make exact
experiments which would be impossible in man. While it is true that
each animal has disorders which are peculiar to itself, and that it is
not subject to some of the disorders to which man is a victim, and,
_per contra_, that man is a victim to some disorders from which animals
do not suffer, yet, taking them as a whole, the diseases of man and of
animals, and the action of remedies on both, are practically identical.
To this I shall have occasion to refer again.