110 CRYSTALLIZABLE NITROGENOUS MATTERS. 



Lehmann found, 1 in experiments on his own person, that the daily 

 amount of urea was increased by a diet of animal food, diminished by 

 one of vegetable food, and reduced to its minimum by a diet consisting 

 exclusively of non-nitrogenous matters, such as starch, sugar, and fat. 

 The comparative results 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 2 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 excre- 

 tion of urea 50 per cent., while it is again restored to its ordinary 

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



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

 formation of the nitrogenous matters of the daily food, but is also, in 

 part at least, derived from the metamorphosis of the more permanent 

 constituents of the body ; since it continues to be discharged, though 

 in diminished quantity, when no food is taken. Lehmann found as 

 much urea in the urine after twenty -four hours of abstinence from all 

 food, as after a diet of non-nitrogenous matters. In the dog, when 

 subjected to entire abstinence, the urea is reduced in three or four days 

 to nearly one-third its former quantity, but is still present in about the 

 same proportion at the end of seven days. In the experiments of Dr. 

 Parkes on a man subjected to a purely non-nitrogenous diet, the daily 

 excretion of urea fell on the second day to 12 grammes, but afterward 

 remained nearly uniform, at rather more .than half that quantity, and on 

 the fifth day still amounted to 7 grammes. Urea has also been found 

 by Lassaigne in the urine of man after continued abstinence from food 

 for fourteen days. 



The quantity of urea has been found by Lehmann, 3 Prof. A. Flint, Jr., 4 

 Parkes, 5 and Yogel 6 to be increased during or after unusual muscular 

 exertion. Other observers (Fick and Wislicenus, Yoit, Ranke) have 

 found no perceptible variation owing to this cause. The same discrep- 

 ancy exists between different writers in regard to creatinine. It is 

 possible that the details of the process by which the albuminous matters 

 during decomposition give rise to the formation of urea are not }^et 

 fully known to us. But it is a matter of common experience, both for 

 man and animals, that continued and laborious muscular activity 



1 Physiological Chemistry. Sydenham edition. London, 1853, vol. ii. p. 450. 



2 Pavy on Food and Dietetics. Philadelphia edition, 1874, pp. 79-81. 



3 Physiological Chemistry. Sydenham edition, vol. ii. p. 452. 



4 New York Medical Journal, June, 1871. 



5 Proceedings of the Royal Society, March 2d, 1871, p. 357. 



6 Neubauer und Yogel, Analyse des "Earns,, 1872, p. 338. 



