THE CIRCULATION OF THE BLOOD, 959 
to be observed that in the case of the foetus and these lower 
groups of vertebrates the brain and anterior parts—that is, 
the most important portions of the animal functionally, 
the parts on which the rest depend for their well-being (since 
the brain is the seat of all the main directive centers)—are 
fed with the best blood the organism possesses, a fact which 
probably explains in part the relatively large size of these 
portions of the body early in fcetal life and throughout its 
duration. 
We now urge upon the student the importance of making 
some observations for himself upon the heart of the frog, tur- 
tle, snake, fish, or other of the cold-blooded animals. At- 
tention should be given chiefly to the functions of the heart, 
though to do this intelligently it must be preceded by some 
study of the anatomy of the organ. It will be understood that 
any directions we may give for the manipulative part of the 
work will be of the simplest kind, and rather suggestive of the 
general method of procedure than intended to illustrate the 
best methods. 
In reality, it is better for exact investigation of the heart 
that no anesthetic be given, and an animal may be rendered 
insensible by a sudden blow upon the head, which, as we shall 
show later, may be painless. However, it will be, upon the 
whole, perhaps, best that the animal be given a few whiffs of 
ether beneath some (glass) vessel, and as soon as it becomes 
insensible, to withdraw the anesthetic, remove or crush the 
head (brain), so that throughout the investigation there may 
be neither interference with the heart from this organ nor any 
doubt about the animal’s insensibility. 
It is well to open the abdomen a little below the heart, so 
that the latter may be exposed, with its pericardium intact, 
when the relations of the heart to the surrounding parts may 
be noticed. 
What strikes every observer is the sluggish. action of the 
hearts of these animals—a great advantage in attempting to 
estimate roughly the relative time occupied by the systole and 
diastole of the different chambers; the peculiar vermiform 
nature of the contraction; the changes of color dependent on 
the degree to which any chamber is filled with blood; and 
many of those minor details important in making up a total 
general impression, but not readily expressed in words. 
After the animal has been bled, the heart’s action may still 
be profitably studied; and, finally, it may be learned that the 
