350 PHYSIOLOGICAL CHEMISTRY. 



thereby being converted into simpler forms of combination 

 which are finally eliminated as waste products. 



It has been shown above how a molecule of glucose which is 

 formed in the plant requires not less than 6 molecules of carbon 

 dioxide, and the same number of molecules of water for its 

 formation, 6 molecules of oxygen being eliminated. A mole- 

 cule of glucose taken into the animal system undergoes the 

 reverse process ; by combining there with 6 molecules of oxygen 

 it is converted into 6 molecules of carbon dioxide and the same 

 number of molecules of water, thus : 



C 6 H 126 + 12 = 6CO 2 + fiH 2- 



Animal food. The food taken by animals is (besides water 

 and a few of its mineral constituents) all derived from vege- 

 tables, but it is taken from them either directly or indirectly; 

 in the latter case it has been previously taken into and assimi- 

 lated by other animals, as in case of food taken in the form of 

 meat, milk, eggs, etc. While some animals (herbivora) feed 

 upon vegetable, and some (carnivora) upon animal food exclu- 

 sively, others are capable of taking and assimilating either. 



The fact that animal food is derived from vegetable matter, 

 renders it superfluous to state that the elements taking an 

 active part in the formation of either vegetable or animal matter, 

 are identical. Of the total number of 66 elements, only 14 are 

 found as necessary constituents of the animal body. These 

 elements are carbon, hydrogen, oxygen, nitrogen, sulphur, 

 phosphorus, chlorine, fluorine, silicium, calcium, magnesium,, 

 sodium, potassium, and iron. A few other elements, such a& 

 aluminium, manganese, copper, etc., are sometimes found in the 

 animal system, but they cannot be looked upon as normal or 

 necessary constituents. 



The various kinds of animal food are derived chiefly from 

 three groups of organic substances, viz., carbohydrates (sugars,, 

 starch, etc.), fats, and albuminous or nitrogenous substances. 

 The inorganic substances, such as phosphates, chlorides, etc. r 

 required by the animal in the construction of bones, for the 

 liberation of hydrochloric acid in the gastric juice, etc., are 

 generally found as constituents of various kinds of food or are- 

 derived from drinking water. Milk contains all the necessary 



