I 



METABOLISM IN FASTING 97 



preliminary fall there occurs a rise in the proteid metabolism, sometimes of 

 considerable size. 



This great diminution in the proteid metabolism in fasting, although occur- 

 ring with various fluctuations, has been verified also for men. In the thirty- 

 day fasting experiment on Succi the N-output on the tenth day was forty-nine 

 per cent of the output at the beginning; on the twentieth day it was thirty-two 

 per cent, and on the twenty-ninth day it was thirty per cent. In men also we 

 meet with this peculiar relationship: the N-output in the urine increases from 

 the third or fourth day, then falls off again (cf. table, page 96). The chief 

 reason for this behavior probably is that on the first day the glycogen deposited 

 in the body spares a part of the proteid from being destroyed ; but since most of 

 the glycogen is used up on this day, so that on the second day its protecting 

 influence has ceased to exist, more proteid is then attacked. In this way the 

 body must become impoverished in available proteid, consequently its destruc- 

 tion falls again and from now on the combustion in the body is maintained to 

 a large extent by the fat, provided the body be not too poor in fat (Prausnitz). 



From facts concerning metabolism after feeding, which will be summa- 

 rized under 4, we know that of all the foodstuffs ingested proteid is the most 

 easily decomposed. Nevertheless in fasting the share of proteid in the total 

 metabolism (calculated in calories) of animals previously well nourished is 

 only seven to seventeen per cent. Inasmuch as this proteid comes from the 

 tissues themselves, it follows that they are not by any means so easily decom- 

 posed as is the food proteid, or more correctly stated, they give up proteid 

 from their own substance only in relatively small quantities. 



The increase in the destruction of proteid which takes place in the later 

 stages of fasting and which continues thence until shortly before death, is. a 

 very interesting phenomenon. Voit, who first observed the phenomenon, ex- 

 plained it by supposing that the fat had all been used up, hence the proteid 

 metabolism was increased in order to keep up the energy requirements of the 

 body. This conclusion was fully confirmed by the following experiment by 

 Rubner. The N-output per day he found to be: first to third day, 1.67 g.; 

 fourth, to fifth day, 1.46 g. ; sixth to eighth day, 3.21 g. The amount of fat 

 burned proved to be: on the second day, 10.3 g.; fourth day, 10.3 g.; eighth 

 day, 2.4 g. 



When at the conclusion of the fast food is again supplied, the body shows 

 a pronounced ability to make good its losses, and now lays on both proteid 

 and fat in large quantities. In the five-day fasting experiment cited above 

 the subject lost during the five days 399 g. proteid, 938 g. fat, 37 g. ash and 

 3,829 g. water. On the succeeding diet, which was a rich one, and of which 

 4,1.41 Cal. were absorbed daily, he destroyed a mean quantity for two days 

 of only 2,424 Cal. daily, and thus recovered in these two days twenty per cent 

 of the lost proteid, thirty-six per cent of the lost fat, seventy-one per cent of 

 the lost water, and sixty-nine per cent of the lost ash. 



C. LOSS OF SUBSTANCE FROM THE DIFFERENT ORGANS 



In fasting the body lives at the expense of its own substance. On purely 

 antecedent grounds it would be most natural to suppose that the organs in 



