20 HUMAN PHYSIOLOGY. 



mainly required for the growth and repair of the tissues. There is good 

 reason to believe that the albuminous principles are decomposed in the 

 body into fat and urea, and the former when oxidized gives rise to the 

 evolution of heat and force, while the latter is eliminated by the kidneys. 

 Muscular work, however, does not result from a destruction of the albu- 

 minous compounds. The oxidation of the carbonaceous compounds, 

 sugars and oils, furnishing the force which is transformed by the muscular 

 system into motor power. When employed exclusively as food for any 

 length of time, the albuminous substances are incapable of supporting life. 



The Saccharine principles are important to the process of nutrition, 

 but the changes which they undergo are not fully understood ; they 

 form but a small proportion of the animal tissues, and by oxidation 

 generate heat and force. Starch undergoes conversion into dextrin and 

 grape sugar. 



The Oleaginous principles form a large part of the tissues of the body. 

 They are introduced into the system as food, and are formed also from a 

 transformation of albuminous matter during the nutritive process; they 

 enter into the composition of nervous and muscular tissue, and are stored 

 up as adipose tissue in the visceral cavities and subcutaneous connective 

 tissue, thus giving roundness to the form and preventing, to some extent, 

 the radiation of heat. While they aid in the reconstruction of tissue, they 

 mainly undergo oxidation, giving rise to the production of heat and the 

 evolution of muscular and nervous force. 



The Inorganic principles constitute an essential part of all animal tissues, 

 and are introduced with the food. 



Water is present in all fluids and solids of the body, holding their 

 ingredients in solution, promoting the absorption of new material into the 

 blood and tissues, and the removal of waste ingredients. 



Sodium chloride is an essential constituent of all tissues, regulating the 

 passage of fluids through animal membranes (endosmosis and exosmosis). 



Calcium phosphate gives solidity to bones and teeth, constituting more 

 than one-half their substance. 



Iron is a constituent of the coloring matter of the blood. 



The Vegetable acids are important to nutrition, and tend to prevent the 

 scorbutic diathesis. 



The Accessory foods also influence the process of nutrition. Tea excites 

 the respiratory function, increasing the elimination of carbonic acid. Coffee 

 is a stimulant to the nervous system ; increases the force of the heart's 

 action, increases the arterial tension and retards waste. 



Alcohol, when introduced into the system in small quantities, undergoes 



