THE FOOD AND DIGESTION 373 



3'4x2 = 6'8 grms. are combined with the nitrogen in the 

 proteid. The remainder, 26'6 grms., go to form fats, the 

 amount of which is 26'6 x 1*3 = 34'6 grms. of fat. 



2. Metabolism during Fasting. 



When the usual supply of energy in the food is cut off, 

 the animal liberates the energy required by oxidising its own 

 stored material and tissues. This is shown by the fact that 

 the animal loses weight and goes on excreting carbon dioxide, 

 urea, and the other waste products of the activity of the 

 tissues. 



Several prolonged fasts have been undertaken by men, and, 

 in one or two of these, careful observations have been made 

 by physiologists. It has been found that during the first day 

 or two of a fast, the individual goes on using proteids and 

 fats at something like the same rate as he did while taking 

 food, but that gradually he uses less and less proteid each 

 day. This is well shown in the case of Succi, who underwent 

 a fast of thirty days. 



Day of Fast. Proteid used in Grms. Fat used. 



1st 104 Not estimated. 



10th 51 170 



20th 33 170 



29th 31 163 



It is from the stored fats that the energy is chiefly derived, 

 and the result of this is that before death the fats of the body 

 are largely used up. The proteid-containing tissues waste 

 more slowly and waste at different rates, the less essential 

 being used up more rapidly than the more essential, which, 

 in fact, live upon the former. In cats deprived of food till 

 death supervened the heart and central nervous system had 

 hardly lost weight ; the bones, pancreas, lungs, intestines, and 

 skin each had lost between 10 to 20 per cent, of their weight, 

 the kidneys, blood, and muscles between 20 to 30, and the 

 liver and spleen between 50 to 70. 



The rate of waste during a fast depends upon the amount 

 of energy required, and it is therefore increased by muscular 

 work and by exposure to cold. When a man is kept quiet 



