596 



METABOLISM, NUTRITION AND DIETETICS 



absolutely free from admixture with carbo-hydrates, which, of 

 course, is not the case with the natural protein foods, will not per- 

 manently suffice for nutrition, but that the protein must be supple> 



mented by a certain amount of carbo- 

 hydrate in some form available for the 

 tissues. It would appear, indeed, that 

 fats are not absolutely indispensable 

 either for maintenance or for growth. 

 White rats have been seen to grow nor- 

 mally over long periods with dietaries 

 devoid of fat ; for example, mixtures of the 

 purified protein edestin (from hemp seed) 

 or casein with starch, sugar, and ' protein- 

 free milk ' freed from fat by extraction 

 with ether (Osborne and Mendel). While 

 in these experiments the food might not 

 have been free from the so-called ' lipoids/ 

 it has been demonstrated that an impor- 

 tant group of substances of this class, the 

 phosphatides, can be synthesized in the 

 body, the necessary phosphorus being ob- 

 tainable even from inorganic phosphates 

 (McCollom). 



Relation between Nitrogen excreted and 

 the Quantity of Protein Food. At this 

 point we may consider a little more 



100 



Fig. 201.- -Curves constructed 

 to illustrate Nitrogenous 

 Equilibrium (from an Ex- 

 periment of Voit's). The 

 loss of flesh in grammes is 



laid off along the horizontal closely a phenomenon already alluded to, 

 axis. The income and and to w hich much discussion used to be 



expenditure corresponding . ,-11 , . i v 



to a given loss are laid off devoted by writers on metabolism. It 

 (in grammes of flesh ') has been stated that within the limits of 

 along the vertical axis. The nitrogenous equilibrium, which is the nor- 



continuous curve is the r 7, , ,., , ,, ,, , -. 



curve of income; the dotted ^al state of the healthy adult, the body 

 curve, of expenditure. With lives up to its income of nitrogen; it lays 

 by nothing for the future. In the actual 

 pinch of starvation the organism, when 



grammes the expenditure its behaviour is tested by a comparison 

 is 492 and the loss 12 of th t k and excretion of nitrogen, 



grammes. Nitrogenous .. , , 



equilibrium is represented appears to have become suddenly econo- 

 as being reached with an mical. When a plentiful supply of protein 

 is presented to the starving body, it seems, 

 judged by the same criterion, to pass at 

 once from extreme frugality to luxury. 



Some flesh may be put on for a short time, some nitrogen may be 

 stored up; but the excretion of nitrogen is soon adjusted to the new 

 scale of supply, and the protein income is apparently spent as freely 

 as it is received. These facts were usually summed up in the 



no income at all the expen- 

 diture is 190 grammes; 

 with an income of 480 



'herf The 1 

 curves cut one another. 



