NUTRITION 



223 



stored in a cell at one time and 

 discharged at another is not 

 fully understood. Some of the 

 conditions under which it is 

 accumulated, and some of those 

 under which it disappears, are 

 known ; but we do not know 

 the whole story. Some 

 people lay up fat in 

 larger quantities than 

 others on the same diet 

 and apparently while do- 

 ing the same amount of 

 work, and some keep 

 lean under conditions ap- 

 parently the most favor- 

 able for growing fat. 



It was formerly be- 

 lieved, and is still some- 

 times supposed, that the 

 animal body forms fat 

 only from the fat of the 

 food; that to get fat we 

 must eat fat. This was 

 disproved by a number 

 of experiments, especially 

 one by Liebig, who kept 

 account over a long period 

 of the fat in the food 

 supplied to a cow, and 

 found that the fat given 

 off in the cow's milk 

 far exceeded that in her 

 food. In another experi- 

 ment four pigs out of a 



FIG. 90 



FIG. 91 



FIG. 92 



FIGS. 90-92. Three successive stages in 



the transformation of ordinary connective 



tissue into adipose tissue 



A portion of the capillary network is shown, 

 surrounded hy the fibers, among which are 

 several cells. The accumulation of fat droplets 

 in the cell cytoplasm is shown in Fig. 91, and 

 the fusion of these upon their increase in size 

 and number to form one large droplet, sur- 

 rounded hy the cytoplasm, is seen in Fig. 92 



