144 ALIMENTATION 



phosphates, sulphates etc.), and frequently with non-nitrogenous matters, 

 especially the carbohydrates. 



The most important nitrogenous alimentary constituents of food 

 are contained in muscular tissue, eggs, milk, the juices of vegetables, 

 cereal grains etc. Among the most important are the following : 

 myosin, the chief proteid constituent of muscle, the various albumins 

 found in eggs and in animal liquids, analogous substances existing in 

 vegetables, casein in milk, a substance sometimes called vegetable 

 casein, vitellin in yolk of egg, fibrin, gelatin, and gluten, an important 

 alimentary substance found in the cereal grains. A distinctive 

 character of these substances is that they contain nitrogen, being com- 

 posed of carbon, oxygen, hydrogen and nitrogen, probably with a small 

 quantity of sulphur. They are either liquid or semisolid in consistence 

 and are coagulable by various reagents. The type of substances of 

 this class is albumin, which has the empirical formula, C 72 H 112 O 22 N 18 S. 

 Certain of these are called proteids, after a hypothetical substance de- 

 scribed by Mulder, under the name of protein. 



Nitrogenous substances are found in animal bodies, as has already 

 been stated. They originate in vegetables by a union of nitrogen, 

 derived chiefly from saline matters, with carbohydrates, the carbohy- 

 drates in vegetables being produced from carbon dioxide and water. 



A distinctive character of nitrogenous matters is that under favor- 

 able conditions of heat and moisture they undergo a peculiar form of 

 decomposition called putrefaction. In the processes of digestion, these 

 substances are converted into peptones, and afterward, it is thought, 

 a part may be changed into leucin, tyrosin and other substances 

 not well defined. An analogous decomposition is said to take place 

 under the influence of dilute hydrochloric acid, at a temperature of 

 104 Fahr. (40 C), and of dilute sulphuric acid, at a temperature of 

 212 Fahr. (100 C.). The chemical history of these substances would 

 require an elaborate description such as properly belongs only to special 

 works on physiological chemistry. 



Non-nitrogenous Alimentary Substances. The important non-nitrog- 

 enous alimentary matters are sugars, starch and fats. These are com- 

 posed of carbon, hydrogen and oxygen. In sugars and starch, the 

 hydrogen and oxygen exist in the proportion to form water, and these 

 matters are therefore called carbohydrates. 



Sugars. Many varieties of sugar occur in food, and this substance 

 may be derived from both the animal and vegetable kingdoms. The 

 most common varieties derived from animals are sugar of milk, and 

 honey, beside a small quantity of liver-sugar, which is taken whenever 

 the liver is used as food. Only a few of the carbohydrates are of 



