FOOD NEEDED BT MAN UNDER VARIOUS CONDITIONS. 473 



that when we wish to diminish the loss of fat or to accumulate fat 

 it takes place in proportions that correspond to the figures of the 

 heat value of the same. This is apparent from the following table. 

 In this we find the weight of the various foods equal to 100 grms. 

 fat, a part determined from experiments on animals and a part 

 calculated from figures of the heat values. 



TABLE XVIII. 



100 grms. fat are equal, to or isodynamic with : 



From Experiments From the Difference, 



on animals. Heat Value. per cent. 



Syntonin 225 213 +5.6 



Muscle-flesh (dried).. 243 235 -j-4.3 



Starch 232 229 -f 1.8 



Cane-sugar 234 235 



Grape-sugar 256 253 - 



From the given isodynamic value of the various foods, it follows 

 that these substances replace one another in the body almost in 

 exact ratio to the potential energy contained in them. Thus in 

 round numbers 240 grms. carbohydrate are equal to or isody- 

 namic with 100 grms. fat, but only in regard to its ability to pre- 

 vent the loss of fat. In regard to the sparing of proteids the 

 carbohydrates accomplish more than the same quantity of fat 

 (page 463). The knowledge of these isodynamic values, as well as of 

 the potential energy in the various foods, is of fundamental impor- 

 tance in the calculation of the diet of human beings under various 

 conditions. 



VI. The Need of Man for Food under Various Conditions. 



Various attempts have been made to determine the daily amount 

 of organic food needed by man. Certain investigators, such as 

 PLATFAIB, MOLESCHOTT, and others, have, from the total consump- 

 tion of food by a large number of similarly-fed individuals, soldiers, 

 sailors, laborers, etc., calculated the average quantity of food 

 required per head. Others, such as PARKES, SMITH, and VOIT, 

 have calculated the daily demand of food from the quantity of 

 carbon and nitrogen in the excreta. Others again, as PETTEK- 

 KOFER and VOIT, have calculated the quantity of nutritive material 

 in a diet by which an equilibrium was maintained in the individual 

 for one or several days between the consumption and elimination 

 of carbon and nitrogen. Lastly, others, especially FORSTER, have 



