438 THE HUMAN BODY. 



tion is a much slower occurrence. Proteids, also, we have 

 learnt from the study of muscle, are probably but little con- 

 cerned in energy-production in the tissues. Speaking 

 broadly, the work of the Body is carried on by the oxidation 

 of carbon and hydrogen, and we find in the Body, in corre- 

 spondence with this fact, two great storehouses of fatty and 

 carbohydrate foods, which serve to supply the materials for 

 the performance of work and the maintenance of the bodily 

 temperature in the intervals between meals, and during 

 longer periods of starvation. One such store, that of car- 

 bohydrate material, is found in the liver-cells; the other, 

 or fatty reserve, is found in the adipose tissue. That such 

 substances are true reserves, not for any special local purpose 

 but for the use of the Body generally, is shown by the way 

 they disappear in starvation; the liver reserve in a few days, 

 and the fat somewhat later and more slowly, but very largely 

 before any of the other tissues has been seriously affected. 

 By using these accumulated matters the Body can work 

 and keep warm during several days of more or less deficient 

 feeding; and the fatter an animal is at the beginning of a 

 starvation period the longer will it live; which would not 

 be the case could not its fat be utilized by the working 

 tissues. Hybernating animals prove the same thing; bears, 

 before their winter sleep, are very fat, and at the end of it 

 commonly very thin; while their muscular and nervous 

 systems are not noticeably diminished in mass. During the 

 whole winter, then, the energy needed to keep the heart and 

 respiratory muscles at work, and to maintain the tempera- 

 ture of the body, must have been obtained from the oxida- 

 tion of the fat reserve with which the animal started. 



G-lycogen. It may have appeared curious to the reader 

 that so large an organ as the liver should be sot apart for 

 the formation of so comparatively unimportant a digestive 

 secretion as the bile ; were this the sole use of the liver 

 its size would certainly be hard to account for. The 

 main function of the liver is, however, a very different 

 one; the formation and storage of a carbohydrate called 

 glycogen, from the abundant food materials carried through 

 it by the portal vein after a meal ; in the times between 



