RESEARCHES ON PROTEID METABOLISM. 143 



So that 42*9 per cent, of the energy of the food has 

 appeared as work. But meat only contains about 80 per 

 cent, proteid, so that 1 grm. N. in proteid enables the doing 

 of 7456 kilogrammetres. Hence 487 per cent, of the 

 energy of proteid taken in as food appears as work — an 

 enormous efficiency. 



As we should expect, this dog required a greater quantity 

 of food when the external temperature was lower, and the 

 amount of heat that had to be produced in the body greater. 

 The experiments described above were made when the 

 external temperature was + 9*5° C. A month later, when 

 the temperature was — 8*9° C, the dog required a larger 

 quantity of meat, in the proportion of 4 to 3. 



When work is done without increasing the food-supply, 

 the body-weight diminishes rapidly at first, and then more 

 and more slowly, until nitrogenous equilibrium is once more 

 established. Under the same conditions, the nitrogenous 

 excretion is increased at first, but not nearly to the same 

 extent as when the animal gets sufficient food. The in- 

 crease in the proteid disintegration now only accounts for 

 \ to ^ of that necessary for the production of the energy 

 expended on doing work. There must hence be a sparing 

 of the expenditure of energy in the other vital processes, so 

 that proteid, which before was used up in some other organs 

 of the body, is now expended in the muscles. In the disin- 

 tegration of the proteid produced by muscular work, the 

 C0 2 is at once eliminated, while the corresponding amount 

 of nitrogen does not appear until the next day, and the 

 increased excretion of urea lasts two or three days (cp. 

 Argutinsky). 



According to Pfltiger, the generally accepted theory 

 that, with a sufficient administration of fat and carbohy- 

 drates, muscular work causes no increased nitrogenous 

 metabolism, is wrong. Even when the animal is putting 

 on fat, increased work causes some increase in nitrogenous 

 metabolism. 



Pfliiger's final conclusion in this paper is of considerable 

 importance. He shows that the metabolic requirements of 

 an animal are conditioned solely by the weight of proteids 



