158 ELEMENTARY AGRICULTURAL CHEMISTRY 



carnine, CyHgN^g, are the chief, and sugar. The ash of 

 muscle consists largely of potash and phosphoric acid com- 

 pounds, but sodium, magnesium, calcium, chlorine and iron are 

 also present. Muscle usually contains from 75 to 78 percent, 

 of water, and 22 to 25 per cent, of solids. Living muscle has 

 an alkaline reaction, but after death it becomes acid, probably 

 owing to the formation of sarcolactic acid, CHg.CHOH.COOH. 

 When a muscle does work the glycogen and sugar, and 

 possibly the fat, are oxidised at an increased rate, and the 

 blood which bathes the muscle receives increased quantities of 

 carbon dioxide. The nitrogenous waste of muscle, which is 

 not now believed to be increased by exertion, is excreted in 

 the form of urea and uric acid. 



Fatty tissue consists of cells, the walls of which are composed 

 of a membrane of albuminjids, filled with fat, which during 

 life is fluid. The fat, which resembles in constitution the 

 vegetable oils already described, contains stearic, oleic and 

 palmitic acids combined with glyceryl. 



Fatty tissue contains water, membranes and fat. in about 

 the following proportions : 



Fat is stored in the body as a reserve from which the animal 

 can draw in times of scarcity of food. It is the most concen- 

 trated form in which energy can be stored. 



Connective tissue, of which tendons, ligaments, cartilage and 

 skin are mainly composed, consists of substances which yield 

 gelatin when heated with water. Three different substances 

 have been recognised, viz., elastin, collagen and keratin. The 

 first is almost free from sulphur, the second contains about 



