16 



STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



isodynamic values to proteins, a number of difficulties were encoun- 

 tered. It was found that an increase of protein in the diet stimulates 

 the total metaboUsm, so that actually more food is utilized and more 

 heat emitted from a diet rich in protein than from one containing 

 little protein. Rubner^ subjected this phenomenon to a very 

 thorough and painstaking investigation and gave it the name of 

 specific dynamic action of proteins. He found that the increase in 

 metabolic activity was greater with proteins than with any other 

 class of foods and that dogs fed on meat respired more actively 

 without doing any external work. After establishing the relation 

 of environmental temperature to metaboUc rate and excluding the 

 reflex increase in metabolism through chemical regulation, Rubner 

 was able to determine the true values of the specific dynamic action 

 of proteins. The ingestion of the starvation requirement for the 

 various forms of food raised the metabolism as shown in table S.^ 



A great advance in the understanding of the specific dynamic 

 action of proteins was made by the investigations of Lusk.^ Instead 

 of using proteins Lusk fed amino-acids. The same action is observ- 

 able with these splitting products of the proteins. It was found 

 that glycocoU and alanine greatly increase the metabolic activity, that 

 leucin and tyrosine exert but a slight effect, and that glutamic acid 

 is without effect. These findings are especially interesting in view 

 of the following facts: It is known that glycocoU and alanine are 

 completely convertible into glucose in the diabetic organism, whereas 

 glutamic acid is so converted that three of its carbons go to form 

 glucose, while the other two carbon atoms are oxidized. When 

 glycosuria is artificially produced by giving phlorihizin, and the 



' Rubner, Max. Die Gesetze des Energieverbraucha bei der Ernaehrung (1902). 



* Rubner, Max. I. c, 325. 



' Lusk, Graham, and S. A. Riche. Animal calorimetry. V, Influence of the ingestion of 

 amino-acids upon metabolism. Jour. Biol. Chem., 13, 155-183 (1912). 

 Lusk, Graham. The cause of the specific dynamic action of protein. Arch. Intern. Med., 

 12, 485-487 (1914). Animal calorimetry: XI. An investigation into the causes of the 

 specific dynamic action of the foodstuffs. Jour. Biol. Chem., 20, 555-617 (1915). 



