222 THE HUMAN MECHANISM 



from the skin. Again, the absorption of some foods, notably 

 proteins or their cleavage products, the ammo-acids, leads to 

 their increased destruction in the cells of the body, just as 

 an open fire burns more vigorously when new fuel is added. 

 Finally, food may be stored within the body. That this is 

 true is shown by the histories of prolonged fasts in which 

 men and women have abstained entirely from food for more 

 than a month. Such fasters steadily lose weight, showing 

 that the body is consuming its own substance. We may 

 therefore pass to the consideration of the storage of material 

 capable of meeting future nutritional needs. 



B. THE FOOD RESERVE OF THE BODY. FAT. 

 GLYCOGEN. CELL PROTEINS 



8. The hoarding of inactive food material. I. The storage 

 of fat. The most obvious reserve food stored in the animal 

 body is fat, which may appear as drops of oil in the cyto- 

 plasm of any cell. Muscle fibers, for example, contain at 

 times large quantities of this substance, and are then said 

 to have undergone fatty degeneration. Under normal condi- 

 tions, however, the presence of considerable quantities of fat 

 in muscle fibers or nerve cells or most gland cells is unusual. 

 In the cells of connective tissue, on the other hand, fat is 

 readily stored under normal conditions, and the adipose tis- 

 sue or fat of the body is simply connective tissue whose cells 

 are loaded with droplets of fat. Figs. 90-92, with their ex- 

 planation, will show how this takes place. But while fat 

 may be normally stored in any of the more open connective 

 tissues, it is especially in the subcutaneous tissue, the great 

 omentum, the mesentery, and some other situations that its 

 chief storage takes place. From these storehouses it is drawn 

 upon as a reserve food material when the immediate supply 

 of food from the alimentary canal becomes inadequate for 

 the work of the body. The exact mechanism by which it is 



