APPENDIX. 
ANIMAL CHEMISTRY. 
AN attempt will be made in this chapter to give a brief account of 
the principal substances entering into or derivable from the mammalian 
body, or resulting from its metabolism. "We may repeat that, inasmuch 
as chemical treatment kills living organisms, we can only know the 
chemical constitution of the dead body. 
The cells and tissues of the body of a mammal are made up of proto- 
- plasm, which belongs to that large class of bodies known as proteids. 
However, it is seldom, if ever, that pure protoplasm is found, for even 
in the youngest cells and in unicellular animals and plants this sub- 
stance usually contains some representatives of the class of bodies known 
as carbohydrates and fats. Protoplasm is, moreover, the producer or 
builder of both fats and carbohydrates, as has been already learned. In 
one sense all the chemistry of the body is the chemistry of protoplasm, 
in that it is either by one or other phase of the metabolism of cells that 
the various secretions, excretions, and reserve products of cells arise. 
We have already considered this aspect of the subject in connection 
with the treatment of the metabolism of the animal body, and shall 
now direct attention in more detail to certain chemical facts, groupings, 
and principles, largely with the purpose of illustrating the resemblances 
between the products of our laboratories and of our bodies. At the 
same time it is to be burne in mind, as we have often remarked in the 
main body of the work, that we are generally unable to say whether the 
syntheses and analyses of the body resemble those made by the chemist 
in the laboratory or not. Indeed, the whole subject, from this point of 
view, is as yet in a very crude condition. 
PROTEIDS. 
These include a large class of bodies as yet very imperfectly under- 
stood chemically. According to Hoppe-Seyler, the following percentage 
composition may be assigned to them : 
oO N H Cc 8 
20°9-28°5, 16°2-17°0, 69-73, 515-545, 0°3-2°0. 
Usually on ignition a very small quantity of ash remains. 
