STATISTICS OF NUTRITION 



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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 

 closely a phenomenon already alluded to, 

 and to which much discussion used to be 

 devoted by writers on metabolism. It 

 has been stated that within the limits of 

 nitrogenous equilibrium, which is the nor- 

 mal state of the healthy adult, the body 

 lives up to its income of nitrogen ; it lays 

 by nothing for the future. In the actual 

 pinch of starvation the organism, when 

 its behaviour is tested by a comparison 

 of the intake and excretion of nitrogen, 

 appears to have become suddenly econo- 

 mical. When a plentiful supply of protein 

 is presented to the starving body, it seeins, 

 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 



Fig. 200. 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 

 axis. The income and 

 expenditure corresponding 

 to a given loss are laid off 

 (in grammes of ' flesh ') 

 along the vertical axis. The 

 continuous curve is the 

 curve of income ; the dotted 

 curve, of expenditure. With 

 no income at all the expen- 

 diture is 190 grammes; 

 with an income of 480 

 grammes the expenditure 

 is 492 and the loss 12 

 grammes. Nitrogenous 

 equilibrium is represented 

 as being reached with an 

 income of about 530 

 grammes; here the two 

 curves cut one another. 



