APPENDIX. 



THE CHEMICAL BASIS OF THE ANIMAL BODY. 



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 association with smaller quantities of various saline and 

 other crystalline bodies. By proteids are meant bodies con- 

 taining 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 other hand of actual "living substance," some- 

 times spoken of as protoplasm (see § 5) in its various modifi- 

 cations, 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 

 death to life, has assumed certain characters and presumably 

 has been changed in construction, but still is proteid matter ; 

 they sometimes speak of protoplasm as "living proteid" or "liv- 

 ing 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 may fairly consider as the 

 nearest approach to native protoplasm, when they can be ob- 

 tained in sufficient quantity for chemical analysis, are found to 

 contain some representatives of carbohydrates and fats as well 

 as of proteids. We might perhaps even go as far as to say, 

 that in all forms of living substance, the proteid basis is found 

 upon analysis to have some carbohydrate and some kind of fat 

 associated with it. Further, not only does the normal food 



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