HEAT EQUIVALENT OF NUTRIENTS OF FOOD. 597 



of albumen containing" 16 per cent of nitrogen would yield 0.857 gm. 

 ofglycocol. The lieat equivalent of glycocol is 3,128 small calories. 

 The heat equivalent of the above quantity is, therefore, 2,681 small 

 calories; or, in other words, 46.95 per cent of the energy of that part 

 of each gram of albumen which is transformed into glycocol is lost to 

 the organism. 



Tlie chemical changes which take place in the animal body are most 

 varied. Sometimes a larger, sometimes a smaller, i^art of the albumen 

 is excreted by the organism unchanged owing to incomplete digestion. 

 Furthermore, a considerable part of the energy is lost to the organism 

 by the formation of the most varied cleavage products. One is thus 

 forced to accept the conclusions which 1 have already pointed out,^ 

 namely, that when the transformation of energy which takes place in 

 the animal organism is to be measured exactly, the heat equivalent of 

 all the i^roducts which enter and are excreted from the organism must 

 be known, and, further, values must not be used in calculations which 

 are based on insufficient experimental data. Instead of this it is bet- 

 ter to be content with less accurate calculations and to take the value 

 found by assuming that urea is the only cleavage product, bearing in 

 mind that thus the real value of the albumen is overestimated. That 

 only the part of the albumen which is digested is referred to here goes 

 without saying. 



liubuer ^ characterizes my standpoint as " a very remarkable con- 

 clusion," with which he finds it difficult to agree. I, for my part, can 

 not believe that it is possible from a single series of experiments, even 

 if it was of five days' duration, to devise a general value for the quantity 

 of energy of albumen which is really utilized. When Rubner finds 

 that a dog on a meat diet loses in the feces and urine 23.2 j)er cent of 

 the energy contained in the albumen consumed, I do not wish to cast 

 the slightest doubt on his figures, but I must still consider it incorrect 

 to apply these figures to other cases where the amount of the feces and 

 the quantity of the cleavage products which are produced along with 

 the urea are entirely different from those in Eubner's experiments. 



I insist, therefore, that in an exact investigation of the metabolism 

 of energy the heat equivalent of the products which enter and are 

 excreted from the body must be determined. If one is not in a position 

 to do this, approximately accurate results will be obtained if the full 

 value of the digestible albumen in the diet is taken. For very many 

 cases this is known, so for each gram of albumen 5,711 small calories 

 are to be added and for each gram of the urea 2,537 small calories are 

 to be deducted from the sum total. The amount of urea can of course 

 be easily and directly determined. There are to be deducted for the 

 heat of solution of urea 21 small calories i)er gram and for each gram 

 of hi[)puric acid 1,311 small calories. The number, 1,311 small calories, 



• Jour, prak, Chem., 44, p. 351. * Ztscbr. Biol., 30, p. 89. 



