200 EXCRETION. 



greater, the proportion of urates is enormous ; and urea is 

 not generally found in this class, but is contained only in 

 the excrements of the rapacious birds, and here only in small 

 quantity. 1 



There are no sufficient reasons for regarding urea as the 

 final result of oxidation of certain of the tissues of the body, 

 uric acid, creatine, etc., being substances in an intermediate 

 stage of transformation ; and we are forced to admit that 

 this principle is formed during the general process of disas- 

 similation, probably from the nitrogenized elements of the 

 body, by a destructive action, with the exact nature of 

 which we are as yet imperfectly acquainted. 



The daily amount of urea excreted is subject to very 

 great variations. It is given in the table as ranging between 

 355 and 463 grains. This is much less than the estimates 

 frequently given; but when the quantity has been very 

 large, it has generally depended upon an unusual amount 

 of exercise, of nitrogenized food, or the weight of the body 

 has been above the average. Parkes gives the results of 

 twenty-five different series of observations on this point. 

 The lowest estimate is 286'1 grains, and the highest 688'4 

 grains. 2 



Compounds of Uric Add. 



Uric acid (C 6 ILN~ 2 O 3 + HO) seldom, if ever, exists in a free 

 state in the normal urine. It is exceedingly insoluble, requir- 

 ing from fourteen to fifteen thousand times its volume of cold 

 water, and from eighteen to nineteen hundred parts of boil- 

 ing water for its solution. 3 It was at one time supposed to 

 exist in the urine in sufficient quantity to give it its acid re- 

 action ; but it has since been ascertained that its solution does 

 not redden litmus. Its presence in the urine uncombined 

 must be regarded as a pathological condition ; still, it is often 



1 MILNE-EDWARDS, Lemons sur la physiologic, Paris, 1862, tome vii., p. 445. 



2 PARKES, 27ic Composition of the Urine, London, 1860, p. 7. 



3 NEUBAUER AND VOGEL, op. cit., p. 27. 



