NUTRITION. 465 



warm-blooded animals have but a small reserve, may "be 

 stored up in the living tissues in such forms that they can 

 utilize it, even when the air-pump fails to extract any from 

 them. But in addition to the supplies for immediate spend- 

 ing, contained in all the cells, we find special food reserves 

 in the Body, on which any of the tissues can call at need. 

 These, especially the oxygen and proteid reserves, are found 

 for most part in the blood. Special oxygen storage is, however, 

 rendered unnecessary by the fact that the Body can, except 

 under very unusual circumstances, get more from the air at 

 any time, so the quantity of this substance laid by is only 

 small; hence death from asphyxia follows very rapidly when 

 the air-passages are stopped; while, on account of the re- 

 serves laid up, death from other forms of starvation is a 

 much slower occurrence. Proteids, also, we have learnt from 

 the study of muscle, are probably but little concerned 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 correspondence 

 with this fact, two great storehouses of fatty and carbo- 

 hydrate 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 laid by in the adipose tissue and to a cer- 

 tain extent in oil droplets found in other cells, and sometimes 

 in blood and lymph. 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 accumu- 

 lated 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. Hibernating animals 

 prove the same thing; bears, before their winter sle p, 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 



