UREA. 345 



670 grains. Dr. John C. Draper 1 found it 408 grains. No urea is 

 to be detected in the urine of very young children ; 2 but it soon 

 makes its appearance, and afterward increases in quantity with the 

 development of the body. 



The daily quantity of urea varies also with the degree of mental 

 and bodily activity. Lehmann and Hammond both found it very 

 sensibly increased by muscular exertion and diminished by repose. 

 It has been thought, from these facts, that this substance must be 

 directly produced from disintegration of the muscular tissue. This, 

 however, is by no means certain ; since in a state of general bodily 

 activity it is not only the urea, but the excretions generally, carbonic 

 acid, perspiration, &c.. which are increased in quantity simultane- 

 ously. Hammond has also shown that continued mental applica- 

 tion will raise the quantity of urea above its normal standard, 

 though the muscular system remain comparatively inactive. 



The quantity of urea varies also with the nature of the food. 

 Lehmann, by experiments on his own person, found that the quan- 

 tity was larger while living exclusively on animal food than with 

 a mixed or vegetable diet ; and that its quantity was smallest when 

 confined to a diet of purely non-nitrogenous substances, as starch, 

 sugar, and oil. The following table 3 gives the result of these ex- 

 periments. 



KIND OF FOOD. DAILY QUANTITY OF UREA. 



Animal 798 grains. 



Mixed 487 " 



Vegetable 337 " 



Non-nitrogenous ...... 231 " 



Finally, it has been shown by Dr. John C. Draper 4 that there is 

 also a diurnal variation in the normal quantity of urea. A smaller 

 quantity is produced during the night than during the day ; and 

 this difference exists even in patients who are confined to the bed 

 during the whole twenty-four hours, as in the case of a man under 

 treatment for fracture of the leg. This is probably owing to the 

 greater activity, during the waking hours, of both the mental and 

 digestive functions. More urea is produced in the latter half than 

 in the earlier half of the day ; and the greatest quantity is dis- 

 charged during the four hours from 6 J to 10 J P. M. 



Urea exists in the urine of the carnivorous and many of the 



1 New York Journal of Medicine, March, 1856. 



2 Robin and Verdeil, vol. ii. p. 500. 



3 Lehmann, op. cit., vol. ii. p. 163. 4 Loc. cit. 



