THE CHEMICAL CONSTITUTION OF THE ANIMAL BODY. 185 
This principle has played a great part in the development of 
man, as we shall show later. 
Weismann’s theories have called attention to the ovum in a 
new and valuable way, though he seems to have given too ex- 
clusive attention to the nucleus (germ-plasma) in itself and 
out of relation to the influence of the countless cells that 
make up the body and must be constantly determining modi- 
fications of the generative organs and the sexual cells them- 
selves; so that Brooks’s explanation, by adding a new factor, 
or, at least, presenting a new aspect of the case, was called 
for and seems to be warranted on the general principle that 
advance in protoplasmic life is dependent on new experiences, 
and that the male cell represents a little world of the concen- 
trated experiences gathered during the lifetime of the or- 
ganism that produced it. But we must consider the whole 
doctrine of gemmules as a crude and entirely unnecessary 
hypothesis. . 
In what sense has the line that evolution has taken been 
predetermined ? In the sense that all things in the universe 
are unstable, are undergoing change, leading to new forms and 
qualities of such a character that they result in a gradual prog- 
ress toward what our minds can not but consider higher mani-. 
festations of being. . 
The secondary methods according to which this takes place 
constitute the laws of nature, and as we learn from the progress 
of science are very numerous. The unity of nature is a real- 
ity toward which our conceptions are constantly leading us. 
Evolution is a necessity of living matter (indeed, all matter) as 
we view it. 
THE CHEMICAL CONSTITUTION OF THE ANIMAL BODY. 
One visiting the ruins of a vast and elaborate building, 
which had been thoroughly pulled to pieces, would get an 
amount of information relative to the original structure and 
uses of the various parts of the edifice largely in proportion to 
his familiarity with architecture and the various trades which 
make that art a practical success. The study of the chemistry 
of the animal body is illustrated by such a case. Any attempt 
to determine the exact chemical composition of living matter 
must result in its destruction; and the amount of information 
conveyed by the examination of the chemical ruins, so to speak, 
