124 TEXT-BOOK OF PHYSIOLOGY 



The Carbohydrates. Carbohydrate principles are reduced during di- 

 gestion to simple forms of sugar, chiefly dextrose and levulose. Under 

 these forms they are absorbed into the blood. These compounds are then 

 carried to the liver and to the muscles where they are dehydrated and stored 

 under the form of starch, termed animal starch or glycogen. Subsequently 

 glycogen is transformed by hydra tion to sugar, after which it is oxidized to 

 carbon dioxid and water. The intermediate stages through which sugar 

 passes before it is reduced to carbon dioxid and water are only imperfectly 

 known. Though a large part of the carbohydrate material is at once oxi- 

 dized, it is now well established that another portion contributes to the forma- 

 tion of, if it is not directly converted into, fat. As the carbohydrates form a 

 large portion of the food, they contribute materially to the liberation of energy. 



The Inorganic Principles. The inorganic principles, though appar- 

 ently not playing as active a part in the metabolism of the body as the organic, 

 are nevertheless essential to its physiologic activity. 



Water is promptly absorbed after ingestion and becomes a part of the 

 circulating fluids blood and lymph. In the digestive apparatus it favors 

 the occurrence of those chemic changes in the food necessary for their 

 absorption, it promotes absorption of the food, holds various constituents 

 of the blood and other fluids in solution, hastens the general metabolism 

 of the body, holds in solution various products of metabolic activity, and, 

 leaving the body through the excretory organs, promotes their elimination. 



Sodium chlorid is absorbed into the blood and, unless taken in excess, 

 is utilized in replacing that which is lost to the organism daily. The exact 

 rdle which sodium chlorid plays in the nutritive process is unknown; but, 

 as it is present as a necessary constituent in all the fluids and solids of the 

 body, and as it is instinctively employed as a condiment, it may be assumed 

 to have a more or less important function. 



When taken as a condiment, it imparts sapidity to the food and excites 

 the flow of the digestive fluids; it ultimately furnishes the chlorin for the 

 hydrochloric acid of the gastric juice. Judging from the impairment of the 

 nutrition as observed in animals after deprivation of salt for a long period of 

 time, it favorably influences the growth and functional activity of all tissues. 



It is well known that herbivorous animals, races of men as well as 

 individuals who live largely on vegetable foods, require a larger addi- 

 tional amount of sodium chlorid than carnivorous animals or human 

 beings who live largely on animal foods, even though the two classes of 

 foods contain relatively the same amounts. The explanation is that the 

 vegetable foods contain potassium salts which, meeting in the blood with 

 sodium chlorid, undergo decomposition into potassium chlorid and sodium 

 carbonate or phosphate, all of which, when in excess, are at once eliminated 

 by the kidneys. The blood, therefore, becomes poorer in sodium chlorid, one 

 of its necessary constituents. 



Potassium phosphate and carbonate are also essential to the normal 

 composition of the solids and fluids. They impart a certain degree of 

 alkalinity to the blood and lymph, one of the conditions necessary to the 

 life and activity of the tissue-cells bathed by them. When administered 

 in small doses, they increase the force of the heart, raise the arterial pressure 

 and increase the activity of the circulation. 



Calcium phosphate and carbonate are partly utilized in maintaining 



