APPENDIX. 



THE CHEMICAL BASIS OF THE ANIMAL BODF. 



THE animal body, from a chemical point of view, may be regarded 

 as a mixture of various representatives of three large classes of 

 chemical substances, viz. proteids, carbohydrates and fats, in associa- 

 tion with smaller quantities of various saline and other crystalline 

 bodies. By proteids are meant bodies containing carbon, oxygen, 

 hydrogen and nitrogen in a certain proportion, varying within narrow 

 limits, and having certain general features ; they are frequently spoken 

 of as albuminoids. By carbohydrates are meant starches and sugars 

 and their allies. We have also seen that the animal body may be 

 considered as made up on the one hand of actual 'living substance,' 

 sometimes spoken of as protoplasm (see 5) in its various modifications, 

 and on the other hand of numerous lifeless products of metabolic 

 activity. We do not at present know anything definite about the 

 molecular composition of the active living substance; but when we 

 submit living substance to chemical analysis, in which act it is killed, 

 we always obtain from it a considerable quantity of the material 

 spoken of as proteid. And many authors go so far as to speak of 

 living substance or protoplasm as being purely proteid in nature : 

 they regard the living protoplasm as proteid material, which in passing 

 from deatfi to life, has assumed certain characters and presumably has 

 been changed in construction, but still is proteid matter; they some- 

 times speak of protoplasm as 'living proteid' or 'living albumin.' It 

 is worthy of notice however that even simple forms of living matter, 

 like that constituting the body of a white corpuscle, forms which we 



