URIC ACID AND ITS 'COMPOUNDS 343 



Notwithstanding the results obtained by Pick and Wislicenus, Frank- 

 land, Haughton, Voit, and others, the fact remains that severe and pro- 

 longed muscular work increases the elimination of nitrogen over and 

 above the quantity to be accounted for by the nitrogenous food taken. 

 Actual observations (Flint, Pavy and others) are conclusive as regards 

 this simple fact ; but it is well known that muscular exercise largely 

 increases the elimination of carbon dioxide and the consumption of 

 oxygen. In exercise so violent as to produce dyspnoea, the distress in 

 breathing probably is due to the impossibility of supplying by the lungs 

 sufficient oxygen to meet the increased demand on the part of the mus- 

 cular system, and the possible amount of muscular work is thereby 

 limited. 



The observations and conclusions of Oppenheim (1880) go far to 

 harmonize the results obtained by different experimenters. Oppenheim 

 concludes that muscular work, when not carried to the extent of pro- 

 ducing shortness of breath or when moderate and extending over a con- 

 siderable length of time, does not increase the elimination of urea ; but 

 that even less work, when violent and attended with shortness of breath, 

 increases the discharge of urea. According to this view, moderate 

 work draws on the oxygen supplied to the body and at once largely 

 increases the elimination of .carbon dioxide ; but the less active processes 

 which result in the production of urea are not so promptly affected. 

 Violent muscular work, however, or work which is excessively prolonged, 

 consumes those parts of the tissues the katabolism of which is repre- 

 sented by the discharge of urea. This view, if accepted, harmonizes 

 the apparently contradictory experiments on the influence of muscu- 

 lar work on the elimination of nitrogen. 



The daily quantity of urea excreted is subject to considerable varia- 

 tions. It is given in the table as 355 to 463 grains (23 to 30 grams). 

 This is less than the estimates frequently given; but when the quan- 

 tity has been very large, it has depended on an unusual amount of 

 nitrogenous food, or the weight of the body has been above the average. 

 Parkes has given the results of twenty-five different series of observations 

 on this point. The lowest estimate was 286.1 grains (18.24 grams), and 

 the highest, 688.4 grains (44.61 grams). 



Uric Acid and its Compounds. Uric acid (C 5 H 4 N 4 O 3 ) seldom if 

 ever exists in a free state in normal urine. It is very insoluble, .re- 

 quiring fourteen to fifteen thousand times its volume of cold water or 

 eighteen to nineteen hundred parts of boiling water for its solution. Its 

 presence uncombined in the urine must be regarded as a pathological 

 condition. 



In normal urine, uric acid is combined with sodium, ammonium, 



