i8o PLANT PRODUCTS 



about 46 per cent, of dry material, the rest being water. 

 The fat of the animal body, like most of the other compounds 

 of this group, is a glycerine ester, and the fatty acids are 

 stearic, palmitic, and oleic. The fat of the animal body as 

 separated by the butcher consists of the chemical fat, 

 enclosed in membranes. In a fat beast the amount of 

 membrane in the fat is comparatively small, but in a lean 

 beast it might amount to one-quarter of the weight of the 

 fat. Carbohydrates are only present to a very small 

 extent. Small quantities of dextrose are always present 

 in the blood, to the amount of about 0*1 to 0*2 per cent., 

 any excess of carbohydrate being stored in the liver. The 

 proteins have been fully described (see Bennett, Bibliography) . 

 During the life of the animal, the chief metabolic changes 

 consist in the hydrolysis of the proteins, fats, and sugars, 

 followed subsequently by their oxidation. The major part 

 of the proteins in the animal body exist in the form of the 

 organs, and are semi-permanent. The remaining portion 

 is temporary, and undergoes rapid chemical changes. It 

 is this portion which supplies the vital energy necessary 

 to the beast. The chief effect of setting an animal to perform 

 work is to increase the rate of chemical breakdown of the 

 fats and carbohydrates. It is only overworking which 

 will produce any large breakdown of the animal proteins. 

 Stimtdants, excitement, and the consumption of salt increase 

 the amount of protein decomposed in the animal body. 

 The heat that is lost by the animal is chiefly lost by radiation 

 and conduction from the surface and by evaporation from 

 lungs and skin. The evaporation from the lungs depends 

 upon the amount of breathing, and, therefore, upon the 

 amount of exercise. 



When the proteins are broken down in the animal body, 

 during the process of digestion, they are resolved into the 

 corresponding amino acids. The number of these amino 

 acids that are necessary is comparatively very limited. 

 Most of the amino acids into which the proteins are broken 

 down in digestion are aliphatic, some mono-carboxylic, 

 and some di-carboxylic. Some of them are mono-amino 



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