122 



METABOLISM AND NUTRITION 



gether 45 Cal. per kilogram, the N-excretion in the urine on the fourth day 

 was reduced to 3 g. The same thing appears from an experiment by Tall- 

 qvist, in which N-equilibrium was recovered just as easily with forty-four 

 per cent of the nonnitrogenous energy supplied by carbohydrates as with 

 eighty-three per cent. Therefore, in the presence of a certain minimum of 

 carbohydrate, fat exercises just as great a N-protection as an isodynamic 

 quantity of carbohydrate, whether N is being supplied in the food or not. 

 The cause of this we shall discuss later. 



We have no detailed experiments to show what conditions favor the greatest 

 total deposit of proteid under the protecting influence of carbohydrates. But 

 considering that the metabolism of proteid runs the same with carbohydrate 

 feeding as with fat feeding, it is probable that there is an agreement in other 

 respects also and that the storage of proteid is greatest when the proportion of 

 carbohydrates to proteids in the food is high. 



These results are of great practical importance, for they show that it is not 

 best to feed a convalescent or a man in a poorly nourished general condition 

 with proteid to the exclusion of other foods. Proteid cannot be deposited, and 

 this means that the organs cannot be built up, on a diet composed only of pro- 

 teid. Plenty of fats and carbohydrates are necessary as well as proteid. 



It is generally supposed to be rather difficult for the adult body to lay on 

 proteid, ajid this is borne out by the fact that N-equilibrium is very quickly 

 established even with a very rich supply of proteid in the food. This behavior 

 is really what one would expect. An excess of proteid would of necessity 

 either raise its percentage in the fluids of the body (blood or lymph), or 

 would be organized into the living protoplasm. The upper limit for the 

 quantity of proteid in the former state is of course soon reached, and if still 

 more proteid is to be retained, it can only be deposited as protoplasm. But, 

 as v. Hoesslin has pointed out, the body seeks to maintain its normal mass 

 of living substance within the narrowest limits possible; because a dispropor- 

 tionately large consumption is associated with the growth of cells, and with 

 this large consumption there goes an increased functional capacity, just as 

 a diminished capacity accompanies a falling off of living substance. The 

 body maintains an average, even level of efficiency by keeping the mass of its 

 functional parts approximately constant. The opposite of this, namely, an 

 intimate dependence of the organism and of its functional state on the amount 

 of protoplasm, or a rapid fluctuation in the mass of the body proteid would 

 not be to the purpose i. e., would be less advantageous than the existing 

 arrangement. For this reason the body destroys most of the excess of proteid 

 which it gets from the food. 



