CHAPTEE XIII. 

 THE ANIMAL. 



THE body of an animal, from a chemical standpoint, consists of a very 

 intimate mixture of compounds, some of which are little understood 

 and apparently highly complex in character. The body may be con- 

 sidered as made up of lifeless products of metabolism (e.g., fat cells, 

 horny matter, earthy portions of bone) permeated by the really 

 living substance, protoplasm. The latter is highly aqueous and con- 

 tains proteids, with smaller quantities of carbohydrates, fats and 

 salts. 



The elements contained in the animal body are the same as those 

 found in plants, but their relative proportions differ considerably. 

 Sodium, chlorine and fluorine particularly appear to be of much 

 greater importance to animals than to plants. 



The proximate constituents of animals also resemble those of 

 plants. 



They may be divided into 



(1) Inorganic compounds, consisting mainly of water, various acids 

 (e.g., hydrochloric acid) and numerous salts (e.g., calcium phosphate, 

 sodium chloride). 



(2) Organic compounds 



(a) Proteids, e.g., albumin, myosin. 



(b) Amides, e.g., urea, and amino- compounds, e.g., creatine. 



(c) Fats. 



(d) Carbohydrates, e.g., glycogen. 



(e) Other compounds. 



The general characteristics of some of these substances have been 

 given in the chapter on the constituents of plants. Eeference must be 

 made to some work on physiological chemistry for further details. 



The chemical composition of the whole bodies of animals was in- 

 vestigated by Lawes and Gilbert in 1848-1859. l 



The table on the following page embodies some of their results. 



It will be seen from the figures that the nitrogenous matter is 

 the most constant in quantity and that the water and fat vary in- 

 versely with each other. The amount of ash is chiefly dependent 

 upon the proportion of bone to the rest of the body. 



1 Jour. Boy. Agric. Soc., 1895. 



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