116 PHYSIOLOGICAL CHEMISTRY. 



excreted by a healthy man is about 35 grammes per day. This amount 

 varies with the size of the body, the average daily proportion of urea 

 to the weight of the whole body being 0.5 per thousand parts. Leh- 

 mann, in experiments on his own person, found the average daily quan- 

 tity to be 32.5 grammes. Bischoff, by similar experiments, found it to 

 be 35 grammes. Hammond, whose weight was 90 kilogrammes, found 

 it to be 43 grammes. Draper, whose weight was 66 kilogrammes, found 

 it 26.5 grammes. 



It has been shown by Draper,* and confirmed by other observers, 

 that there is 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 confined to the bed during 

 the whole twenty-four hours, as in the case of a man with fracture of 

 the leg. Its production is less abundant during the forenoon than 

 in the afternoon or evening, the maximum occurring from 3 to 5 hours 

 after the principal meal of the day. 



An important variation in the daily excretion of urea is that which 

 corresponds with the kind and quantity of the food. Urea is the prin- 

 cipal representative of the decomposition of the nitrogenous ingredients 

 of the body, as it is the only substance containing nitrogen which is 

 discharged in any considerable amount by the excretions. A compari- 

 son of the nitrogen contained in the daily food with that discharged 

 from the body in various forms shows that fully 85 per cent, reappears 

 as an ingredient of the urea ; the remaining 1 5 per cent, being con- 

 tained in the uric and hippuric acids and creatinine of the urine, and 

 in the nitrogenous matters of the feces. 



All observers agree that the quantity of urea excreted varies in pro- 

 portion to the nitrogenous matters contained in the food. Lehmannf 

 found in experiments on his own person, that the daily amount of 

 urea was increased by animal food, diminished by vegetable food, and 

 reduced to its minimum by a diet consisting exclusively of non-nitro- 

 genous matters, such as starch, sugar, and fat. The comparative re- 

 sults were as follows : 



Kind of diet. Daily quantity of urea. 



Mixed ........ 32.5 grammes. 



Animal 53.2 



Vegetable 22.5 



Non-nitrogenous ...... 15.4 " 



It also appears, from the observations of Mahomed, J that the influence 

 of a change of diet in this respect is manifested very rapidly ; twenty- 

 four hours of a non-nitrogenous diet being sufficient to reduce the 

 excretion of urea 50 per cent., while it is restored to its ordinary stand- 

 ard within three or four hours after the use of animal food. 



Urea, however, does not depend exclusively on the direct trans- 



* New York Journal of Medicine, March, 1856. 



f Physiological Chemistry, Sydenham Edition. London, 1853, vol. ii., p. 450. 



J Pavy, Food and Dietetics, Philadelphia Edition, 1874, pp. 79-81. 



