888 



METABOLISM. 



Urea Excretion in Grammes per Diem. 



to vary greatly with different dogs; small animals metabolise more 

 proteid per kilo, than large ; lean animals more than fat. Small dogs 

 have a larger proportionate surface, and relatively a smaller amount of 

 body-fat. 1 



Many similar observations have been made on fasting men. One 

 of these (Cetti) was under observation at different times and by 

 different observers. His weight was about 57 kilos. The amount of 

 urea excreted per diem, during the first ten days of fasting, was a little 

 over 20 grms., equivalent to from 10 to 11 grms. N. Another (younger) 

 man, weighing about 60 kilos., was also found by I. Munk to excrete per 

 diem, during the first ten days of fasting, about 11 grms. N, representing 

 an average loss per diem of about 70 grms. proteid. In these cases there 

 was but little body-fat. In other individuals, in which there was abund- 

 ance of body-fat, the N excreted has been found to be much less. Thus 

 Succi (weight 63 kilos, at beginning, 52 kilos, at end of period) was found 

 by Luciani, during a thirty days' fast, to excrete on the tenth day 

 67 grms. ; on the twentieth, 4'3 grms. ; and on the last day 3 -2 grms. N ; 

 and Jacques (62 kilos.), observed by Noel Paton and Stockman, gave an 

 average daily loss of 5*29 N. Praussnifcz determined the amount of N 

 excreted by ten persons during the second day of fasting, and found the 

 average, for a man weighing about 70 kilos., to be 13*7 grms., equivalent 

 to a loss of 90 grms. proteid per diem, or about 1*2 grms. per kilo, 

 body weight. This may therefore be regarded as representing the 

 amount which it is absolutely necessary to supply in the food, for the 

 maintenance of nitrogenous equilibrium. 



In herbivora there may be an actual increase in the nitrogenous excreta 

 at the beginning of a starvation period, instead of a diminution ; due to 

 the fact that, under these circumstances, such animals, being reduced to living 

 upon their tissues, become practically carnivorous. As in carnivora, such 

 increase may become greater towards the end of inanition, in consequence of 

 the exhaustion of the fat of the body, and an increased destruction of the tissue 

 proteids. 2 



Now, the amount of urea in the urine during a fasting period of not 

 too long duration is probably a definite measure of the necessary de- 

 struction of tissue proteid which goes on within the body, and it may 

 therefore be taken as a result of such experiments, that the amount of 

 this metabolism is fairly constant. Such destruction occurs in spite of 



1 Rubner, Ztschr. f. BioL, Miinchen, 1883, Bd. xix. S. 535. 



2 Rubner, ibid., 1881, Bd. xvii. S. 214 ; Heymans, Bull. Acad. roy. d. sc. de Bely., 

 Bruxelles, 1896, p. 38. 



