CH. XXV.] CARBOHYDRATES. 385 



1. Various groups of alcohols and organic acids, and their com- 

 pounds, such as the fats and carbohydrates. 



2. Various derivatives of ammonia, amides, amines, urea, &c. 



3. Aromatic bodies, or derivatives of benzene. 



4. Proteids, the most important of all, and substances allied to 

 proteids, like the albuminoids, pigments, and ferments. 



Many of these substances we shall study with the blood, food, 

 urine, fec. 



A more convenient practical method of grouping physiological 

 proximate principles is the following : 



( Water. 



Inorganic . . . < Salts e.g. chlorides and phosphates of sodium 

 I and calcium. 



Organic 



( Proteid* e.g. albumin, myosin, casein. 



j.. | Albuminoids e.g. gelatin, chondrin, nuclein. 



' "I Simpler- nitrogenous bodies e.g. lecithin, 



creatine. 



f Fats e.g. butter, fats of adipose tissue. 

 I 



Non-nitrogenous \ ^^^tt;^ S S 

 acids. 



I Simple organic bodies e.g. cholesterin, lactic 



Many of the substances enumerated above only occur in small 

 quantities. The most important are the inorganic substances, 

 water and salts ; and the organic substances, proteids, carbo- 

 hydrates, and fats. It is necessary in our subsequent study of 

 the principles of chemical physiology that we should always keep 

 in mind this simple classification ; the subdivision of proximate 

 principles into proteids, fats, and carbohydrates forms the 

 starting-point of chemical physiology. 



Carbohydrates. 



The carbohydrates are found chiefly in vegetable tissues, and 

 many of them form important foods. Some carbohydrates are, 

 however, found in or formed by the animal organism. The most 

 important of these are glycogen, or animal starch; dextrose ; and 

 lactose, or milk sugar. 



The carbohydrates may be conveniently defined as compounds 

 of carbon, hydrogen, and oxygen, the two last-named elements 

 being in the proportion in which they occur in water.* 



They may be for the greater part arranged into three groups 

 according to their empirical formulae. The names and formulae 



* Tliis definition is only a rough one, and if pushed too far would include 

 several substances like acetic acid, lactic acid, and inosite, which are not 

 carbohydrates. 



K.I'. C 



