METABOLISM 



273 



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

 tissues. 



Prolonged fasts have been borne by both men and animals, 

 and, in one or two of these in man, careful observations have 

 been made by physiologists. It has been found that during 

 the first day or two of a fast, the organism draws most lavishly 

 on its store of carbohydrates, and that there is a marked 

 diminution in the protein metabolism. As soon as the 

 carbohydrate depots are exhausted, the protein metabolism 

 suddenly increases, to fall slowly as the fast progresses. Fat 

 metabolism falls slowly throughout the fast. The follow- 

 ing figures obtained by Benedict on a subject who fasted 

 for thirty-one days clearly demonstrates the effect of fasting. 



Amount of Proteins, Fats, and Carbohydrates in grms. 

 cataholised in twenty-four hours during a fast. 



(1) 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 to a great extent used up. (2) The protein- 

 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 scarcely lost weight ; the bones, pancreas, 

 lungs, intestines, and skin each lost between 10 and 

 20 per cent, of their weight, the kidneys, blood, and muscles 

 between 20 and 30, and the liver and spleen between 50 

 and 70. 

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