INFLUENCE OF FOOD ON METABOLISM 



107 



E. SUMMARY AND DISCUSSION 



It appears from the experimental facts brought together under divisions 

 Be to De, that the ingestion of proteid always raises metabolism to a con- 

 siderable extent, whereas ingestion of fat and carbohydrates either produces 

 no increase, or at most only a slight one. 



The experiments of Pettenkoifer and Yoit, from which these conclusions 

 are drawn, were not carried out in a continuous series, and it is possible that 

 the result was due in part to the changed condition of the animal. The follow- 

 ing series by Kubner is, therefore, more decisive, because the experiments came 

 one immediately after the other: 



In fasting (days 2, 4, 6 and 8) the average metabolism was 40.4 Cal. per kg. 

 of body-weight; on feeding 56.8 g. N it was 44.8 Cal. per kg.; with 167 g. fat, 

 40.9 Cal. ; and with 411 g. carbohydrate, 42.3 Cal. The percentage increase over 

 the fasting metabolism was therefore 11.9 for proteid, 1.2 for fat, and 4.2 for 

 carbohydrate although, as is evident from the table, the heat value of the food 

 in all cases was almost exactly the same. 



In another series on feeding 1,500 g. meat Rubner found an increase of 

 24.3 per cent over the fasting metabolism, and on feeding- 153 g. lard or 456 g. 

 carbohydrates, an increase of 5.1 per cent. 



The results of Pettenkoffer and Voit are abundantly confirmed by these 

 more recent experiments. 



In explanation of the fact that increasing the supply of food produces, 

 under certain circumstances, an increase in the metabolism, we might suppose 

 either that the greater store of combustible material itself induces a more 

 extensive combustion, or that the increase of total metabolism is due to the 

 work of digestion or to muscular movements, etc. The matter can be definitely 

 settled only by experiments on men where the voluntary movements can be 

 controlled. 



Both Magnus-Levy and Koraen have made such experiments and have 

 shown that a clearly marked increase in the metabolism of the resting body 

 makes its appearance only after ingestion of proteid. This increase, however, 

 is scarcely to be ascribed to the work of digestion, but is rather the expression 

 of a special property [what Kubner calls " specific dynamic action " ED.] 

 of proteid to intensify the metabolism independently of muscular movements. 



Nevertheless, it should not be asserted that the work of digestion causes 



