132 A. I. RINGER 



cell. The greater the amount of food brought to the cell, the more was it 

 stimulated to catabolize it. 



Rubner, Zuntz and Lusk have performed a great many experiments 

 which may 'throw light on the cause of this increase in metabolism. Be- 

 cause of the specificity of each foodstuff to stimulate metabolism, Rubner 

 called it the ''specific dynamic action" of the foodstuffs. He believes that, 

 localise the carbohydrates and fats are directly available to the cells for 

 their nutrition there is therefore comparatively little increase in heat pro- 

 duction after their ingestion. In the case of protein, however, it can con- 

 tribute to the cell metabolism only in so far as it can give rise to glucose, and 

 all the intermediary products which cannot go over into glucose are burnt, 

 but their heat is given off as free heat and cannot be used by the cells. 



Lusk proceeded to look for the cause of the specific dynamic action 

 of the proteins along new lines. He realized that in order to analyze 

 the action of protein on metabolism, one must take up the study of the 

 influence of the individual amino acids, for it is they which come in 

 intimate contact with the cells of the body. Then he reasoned thus: if 

 Rubner's hypothesis be correct that the fraction of the protein molecule 

 which goes over into glucose is the one which contributes to the life of 

 the cell, and that the fraction which does not go over is burned, giving 

 rise to free heat then amino acids like glycocoll and alanin, which are 

 completely converted into glucose, should exert no specific dynamic influ- 

 ence at all, whereas glutamic and aspartic acids, which contribute only 

 three of their carbons to glucose formation, should have a marked dynamic 

 effect. Also, substances like leucin and tyrosin, which do not give rise to 

 any sugar, should have a most pronounced dynamic effect. 



Experiments not only failed to lend any support to Rubner's theory, 

 but revealed just the contrary of what was expected. Glycocoll and alanin 

 were found to possess a very pronounced power of stimulating metabolism 

 nnd heat production. Leucin and tyrosin possess that power to a lesser 

 extent, and aspartic and glutamic acids have none at all. 



In another series of experiments Lusk found that the administra- 

 tion of 5.5 grams of glycocoll raised the heat production of a dog 7.3 

 per cent and 5.5 grams of alanin raised it 7 per cent. When he gave the 

 two amino acids together there was a summation of influences and the 

 heat production wa's raised 18 per cent. Ten grams of glycocoll caused 

 a rise of 15.0 and 17.5 per cent in two successive experiments, and the 

 giving of 20 grams of glycocoll caused a rise of 33.5 and 34.0 per cent in 

 two experiments. Similar results were obtained after administering 20 

 and 30 grams of alanin. 



These experiments prove beyond any question that the stimulus these 

 ammo acids exert is directly proportional to the amount of material ad- 

 ministered. 



Since glycocoll and alanin have been shown to be completely converted 



