32 



MAINTENANCE KATIONS OF FARM ANIMALS. 



tains potential energy equal, according to Ostwald, to 3.319 calories per gram 

 in the gaseous state. If we assume that the alanin yields lactic acid with a 

 heat of combustion of 3.7 calories per gram we may make the following com- 

 parison : 



Calories. Calories. 



Energy of 1 gram alanin 4. 356 



Energy of 1. Oil grams lactic acid 3. 742 



Energy of 0. 191 gram ammonia 0. 634 



4.376 



Difference . 020 



In other words, it would appear that the deamidization of the amino acids, 

 like the antecedent cleavage of the proteins, is a nearly isothermic reaction and 

 that we must seek elsewhere for the explanation of the specific dynamic effect 

 of protein. We can by no means assert, however, that the protein katabolism 

 actually takes place according to this simple scheme, nor that the nonnitrog- 

 enous substances resulting from deamidization of the amino acids yield their 

 energy without loss. It seems not unlikely that the higher fatty acids and other 

 nonnitrogenous derivatives of protein are broken down by cleavage and other- 

 wise to comparatively simple molecules before they are finally oxidized, and 

 there is the possibility of more or less loss of energy in such processes. 



As already indicated, Rubner explains the specific dynamic effect of protein 

 from the foregoing point of view, but in a different manner. It has been shown 

 beyond reasonable doubt that sugar is produced, or may be produced, in the 

 katabolism of protein. According to Rubner, it is only the energy of this sugar 

 that is capable of being used for the physiological functions of the body cells, 

 while the energy set free in the conversion of protein into sugar is liberated as 

 heat and constitutes the specific dynamic effect. This explanation of Rubner's, 

 however, seems to be disproved by recent results reported by Lusk and Ringer. 1 

 They have shown that alanin is completely convertible to dextrose in a diabetic 

 animal, while in the case of glutamic acid but three out of the five carbon atoms 

 of the molecule are utilized for the production of dextrose. According to Rub- 

 ner's hypothesis, therefore, alanin should show no specific dynamic effect, while 

 glutamic acid should show a considerable one. In a preliminary communication 

 Lusk 2 reports that neither one of these amino acids when added to a standard 

 diet increased the excretion of carbon dioxid in the respiration. This result is 

 in striking contrast with those of Falta, Grote, and Sttihlein and of Zuntz and 

 Mering just referred to, in which the crude products of tryptic or peptic diges- 

 tion were fed. They suggest that some substance other than the recognized 

 ammo-acids may be responsible for the stimulating effect of protein upon metabo- 

 lism, while they likewise recall the fact that crude peptones have been found to 

 have a poisonous effect when injected intravenously while purified peptones do 

 not, and likewise the fact that in Zuntz and Mering's experiments purified 

 peptones caused no increase in the metabolism. 



EXCRETION. 



Zuntz 3 calls attention to Barcrof t's 4 experiments, which show that the excre- 

 tory activity of the kidneys is accompanied by a notable increase in the 

 amount of oxygen consumed, and sees in the work thrown on these organs 

 by the elimination of the nitrogen of protein one of the causes of its specific 



1 Journal of the American Chemical Society, vol. 32, p. G71. 



2 Proceedings of Society for Experimental Biology and Medicine, 1910, vol. 7, p. 136. 

 ■■ Medizinsche Klinik. 1910. 



* Ergebnisse der Physiologie, vol. 7, p. 744. 



