CHEMICAL CONSTITUENTS OF BODY AND FOOD. 25 



alimentary canal and used for the support of life, by supplying the 

 waste continually occurring in the living animal tissues, and also 

 weight, heat, and energy. Food contains substances that have a cer- 

 tain chemical relation to the tissues which it supports. The sub- 

 stances out of which the complex adult tissues are constructed are 

 chemical elements, chemical compounds, or unions of these elements. 

 The food taken in by the animal consists of the same or similar com- 

 position, in its nature very complex. 



Animals are either carnivorous or herbivorous. The carnivora, 

 or flesh-eating species, consume food possessing apparently the same 

 chemical components as the tissues and fluids of their own bodies. 

 The food of the herbivora, or vegetable-eating species, contains prin- 

 ciples resembling very closely those found in the animal body. Xo 

 matter what the source or nature of the food for animals might be, 

 their chemical constituents or principles are similar, since it is 

 through the agency of the vegetable kingdom with the aid of light 

 and heat from the sun that the simpler combinations of inorganic 

 nature are woven together and elaborated to form the complex organ- 

 isms in the shape of plants and vegetables. Thus, the animal king- 

 dom is dependent on the vegetable for its existence ; numerous experi- 

 ments have proven that the animal organism does not possess the 

 power to any great extent of constructing complex from simple mate- 

 rials. Yet complex foods it must have to supply its own complex con- 

 stituents. However, it is also necessary that the food should possess, 

 besides the .complex constituents, a proper proportion of the various 

 principles, and these must be in a digestible form. It is well known 

 that beans, peas, and other vegetables contain a very considerable 

 percentage of proteid, but it is in such indigestible form, that much 

 of it passes off in the faeces. The various digestive juices had been 

 unable properly to dissolve their nutritive elements. 



Of the 80 elements known to the chemist, but 20 are found in 

 the body. They are: carbon, hydrogen, nitrogen, oxygen, sulphur, 

 phosphorus, fluorin, chlorine, iodine, silicon, sodium, potassium, cal- 

 cium, ammonium, magnesium, lithium, iron, and occasionally man- 

 ganese, copper, and lead. These elements are rarely found in the 

 free state, being usually in the form of compounds. 



The compounds, or, as they are sometimes termed, proximate 

 principles, are divided into: (1) mineral, or inorganic, compounds; 

 (2) organic compounds, or compounds of carbon. The organic com- 

 pounds may again be divided very conveniently into two groups : the 

 nitrogenous and nonniirogenous. 



