CRYSTALLIZABLE NITROGENOUS MATTERS. 117 



formation of nitrogenous matters in the food, but is also 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 absti- 

 nence, the urea is reduced in three or four days nearly to one-third its 

 former quantity, but is still present in about the same proportion at the 

 end of seven days. In the experiments of Parkes on a man subjected 

 to 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 T grammes. Urea has also been found by Lassaigne in the urine of 

 man after continued abstinence from food for fourteen days. 



Yery contradictory statements have been made in regard to the influ- 

 ence of muscular exertion on the production of urea. By some observers 

 (Lehmann, Flint, Weigelin, Parkes, and Yogel) the urea has been found 

 to be increased during or after unusual bodily activity ; by others (Fick 

 and Wislicenus, Yoit, Ranke) it has been denied that muscular exertion 

 causes such an effect. This discrepancy has resulted mainly from not 

 taking into account the increase or diminution of nitrogenous food 

 simultaneously with the periods of muscular rest or activity. There 

 can be no doubt, since the observations of Flint* on the pedestrian 

 Weston, afterward repeated by Pavy,f on the same person, with essen- 

 tially similar results, that the production of urea in man is considerably 

 increased by muscular exertion, and that this increase is over and above 

 what can be accounted for by the nitrogenous food consumed. It must, 

 therefore, be attributed to the functional activity of the muscular system ; 

 and as this system forms no less than 40 per cent., by weight, of the 

 entire frame, it will account for a considerable portion of the urea pro- 

 duced. It is, also, a matter of common experience, both for man and 

 animals, that continued and laborious muscular activity requires a cor- 

 responding supply of nitrogenous food; and the final result of the 

 internal metamorphosis of such substances is mainly represented by 

 urea. 



10. Sodium TJrate, C 5 H 3 N 4 O 3 Na. 



As its name indicates, this is a saline body, consisting of a nitro- 

 genous organic acid, namely, uric acid (C 5 H 4 N 4 3 ), in union with so- 

 dium. A portion is also in combination with potassium, but the sodium 

 salt is in much the greater quantity. The urates are found normally 

 only in the urine, where they exist in the proportion of about 1.45 parts 

 per thousand. The entire quantity of uric acid excreted by a healthy, 

 full-grown man, is about 0.7 gramme per day. It is, therefore, very 

 much less abundant than urea ; and, according to the researches of Ranke, 



* New York Medical Journal, June, 1871. 

 f London Lancet, 1876, vol. ii., p. 848. 



