156 THE BODY AT WOEK 



no consumption of proteins as fuel when cheaper fats and sugar 

 would answer equally well. In the case of Succi, who fasted 

 for thirty days, the nitrogen excreted fell to 6-7 grammes on the 

 tenth day, to 4-3 grammes on the twentieth, and to 3-2 grammes 

 on the last day. Clearly, we have to make a distinction, when 

 all food is cut off, between the oxidation of the protein which, 

 failing all other material, is withdrawn from the tissues for the 

 purpose of supplying the force absolutely necessary to maintain 

 respiration and such other movements as are inevitable, and 

 to keep up the temperature of the body force which under 

 other circumstances might be supplied by non-nitrogenous 

 food and the oxidation to which bioplasm is inevitably 

 subject, so long as it is alive. The oxidation of bioplasm 

 under ordinary circumstances of course supplies force ; but 

 it does not follow that this is sufficient to maintain the 

 respiratory movements and the contraction of the heart. 

 When a herbivorous animal is starved, it not infrequently 

 excretes more urea at the commencement of the starvation 

 period than it was excreting when well fed. Its activities 

 did not come to a standstill when carbohydrate food was cut 

 off. For a time they were maintained at the expense of its own 

 tissues. On the other hand, the results obtained from the 

 observation of the man who went without food for thirty days 

 show that Nature is able to economize force by reducing the 

 metabolism of living substance below the normal. It might 

 be supposed that the irreducible metabolism could be ascer- 

 tained by giving a nitrogen-starved animal non-nitrogenous 

 food, but it is found that this scarcely affects the tissue-waste. 

 Becoming more active, the tissues, while saved from the neces- 

 sity of supplying fuel for the production of heat and motion, 

 suffer more waste. Again, it might be expected that if to an 

 animal which had been starved for a few days, until its urea 

 had fallen to the starvation limit, exactly sufficient protein 

 were given to supply this amount, the tissues would be saved. 

 It is found, on the contrary, that nearly twice as much urea 

 is excreted as before. If the quantity of protein be steadily 

 increased, equilibrium is at last established, but not until 

 the amount of nitrogen in the protein given is two and a half 

 times as great as the amount excreted during the starvation 

 period. Additional food at once gives rise to additional 



