16 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



before it is taken as food. Boiling bursts the cellulose envelopes of 

 the starch grains, and so allows the digestive juice to get at the 

 starch proper. Cellulose is found in a few animals, as in the test or 

 outer investments of the Tunicates. 



For further information regarding the carbohydrates see Lesson XIII. 



THE FATS 



Fat is found in small quantities in many animal tissues. It is, 

 however, found in large quantities in three situations, viz. bone 

 marrow, adipose tissue, and milk. The consideration of the fat in 

 milk is postponed to Lesson IV. 



Via. 5. — A few cells from the margin of a fat lobule ; /. rf., fat globule distending fat cell : n, nucleus : 

 m, membranous envelope of the cell ; cr., bunch of crystals within a fat cell ; c, capillary vessel ; 

 «, venule ; c. ^, connective tissue cell. The fibres of the connective tissue are not represented. 



The contents of the fat cells of adipose tissue are fluid during life, 

 the normal temperature of the body (37° C, or 99° F.) being con- 

 siderably above the melting-point (25° C.) of the mixture of the fats 

 found there. These fats are three in number, and are called palmitin, 

 stearin, and olein. They differ from one another in chemical com- 

 position and in certain physical characters, such as melting-point 

 and solubilities. Olein melts at —5° C, palmitin at 45° C, and stearin 

 at 53-66° C. Thus, it is olein which holds the other two dissolved at 

 the body temperature. Fats are all soluble in hot alcohol, ether, and 

 chloroform, but insoluble in water. 



Chemical Constitution of the Fats.— The fats are compounds of 



