XIII. 



THE ANIMAL 



271 



The proportions of valuable manurial substances in bones has 

 already been given. 1 



The Fatty Tissue. This consists of cells, the walls of which are 

 composed of a proteid substance resembling elastin, filled with fat 

 which, during life, is in the fluid state. The fat consists mainly of 

 glyceryl esters of stearic, oleic, palmitic, and other fatty acids; but, 

 in addition, free fatty acids are present in small amount. Animal fats 

 resemble in constitution the vegetable oils already described. 2 



Fats from different animals, or even from different parts of the 

 same animal, have very different properties, especially as to consis- 

 tency and melting-point. These depend upon the relative amount of 

 the glycerides of high melting-point (e.g., stearin, melting-point about 

 63, and palmitin, melting-point 62), and those of low melting-point 

 (olein, melting-point about - 5). 



The average proportions of fat, water and membrane (cell walls, 

 etc.) are given by Hammarsten as follows : 



Fat may be produced in the animal from the fat, proteids or carbo- 

 hydrates contained in the food. It forms a valuable reserve, from 

 which the animal can draw in times of scarcity of food, being the 

 most concentrated form in which energy can be stored in the body. 



Muscle. Muscular fibre consists of a sheath composed of elastin 

 and the contents, mainly albumins. 



Myosin is the principal albuminous constituent of the dead muscle. 

 Its amount varies from 3 to 1 1 per cent. It is a globulin, is soluble 

 in neutral salt solutions, and coagulates at 56. 



Other albuminoids are found in muscle, of which musculin, muscle- 

 stroma and myoglobin are the chief. 



There are also "nitrogenous extractives" present, the chief being 

 creatine, (methyl-guanidine acetic acid), NH : C(NH 2 ).N(CH 3 ).CH.,. 

 COOH + H. 2 O ; hypoxanthine or sarcine, C 5 H 4 N 4 O ; xanthine, 

 C 5 H 4 N 4 O., ;~ guanine, C f ,Hr,Nr,O ; and car nine, C 7 H 8 N 4 O ? + H 2 O. 



These substances constitute the chief ingredients of the various 

 commercial " extracts of meat ". Though they cannot apparently act 

 as true foods, they have an important function to play with regard to 

 the palatability and digestibility of the foods in which they occur. 



Muscle also contains inosite or inositol, C t} H 12 O + H O (hexahy- 

 droxy-hexamethylene), glycogen, C 6 H 10 O fl , a sugar (probably glucose 

 and most likely formed, after death, from glycogen), and sarcojactic 

 -acid, CH 3 .CH(OH).COOH. Fat is also present, together with lecithin. 



Vide p. 127. 



2 Vide p. 197. 



