142 SCIENCE PROGRESS. 



that muscular work does give rise to a definite increase in 

 the excretion of urea. This increase, however, is observed, 

 not on the day on which the work is performed, but on 

 the two succeeding days. He calculates that the increased 

 oxidation of proteid, evidenced by the extra secretion of 

 urea, will account for the energy expended on the days on 

 which work was done. The work consisted in climbing, 

 on four separate occasions, to a height of iooo to 1300 

 metres, and the expeditions lasted from five to eight hours. 

 In (2), Pfl tiger, on the ground of experiments performed 

 on dogs, re -affirms Liebig's dictum, i.e., that proteid is the 

 chief, if not the only source of muscular energy. He em- 

 ployed a lean dog, weighing about 30 kilos., which he fed 

 on nearly pure proteid diet (lean meat). The amount of fat 

 and carbohydrate contained in the meat was not sufficient 

 even for the work of the heart. On this diet he found that 

 the dog could work perfectly well, and was in an excellent 

 state of health at the end of some months, showing that, in 

 this case, the energy for the production of muscular work 

 (drawing a cart) must have been afforded by the com- 

 bustion of proteids. In the experiments, periods of rest 

 alternated with periods of severe work. The amount of 

 meat required to maintain the dog's weight constant and 

 nitrogenous equilibrium was first ascertained for a period 

 of rest. If the dog was then made to do a certain amount 

 of work on the same diet, the output of nitrogen excreted 

 became larger than the income, and the dog lost weight. 

 In order to maintain a condition of equilibrium, it was 

 necessary to increase the amount of meat, and the increased 

 food required was proportional to the amount of work 

 done. Thus when the dog performed 109,608 kilogram- 

 metres, he required 496*5 grms. meat more than during a 

 resting period. This meat contained 15*98 grms. N. From 

 this he concludes (allowing for the small amount of fat in 

 the meat) : — 



1 grm. N. = 6409 kilogrammetres. 

 According to Rubner : — 



1 grm. N. in meat in combustion = 14,909 kilogram- 

 metres. 



