URIC AC1U AJ\L> UR&A. 



45 



phosis ; and, except the sulphur and phos- 

 phorus, both of whiph are probably oxidized, 

 no element is separated. 



This form of metamorphosis is applicable 

 to the vital transformations in the lower 

 classes of amphibia, and perhaps in worms 

 and insects. In the higher classes of ani- 

 mals the uric acid disappears in the urine, 

 and is replaced by urea. 



The disappearance of uric acid and the pro- 

 duction of urea plainly stand in a very close 

 relation to the amount of oxygen absorbed in 

 respiration, and to the quantity of water con- 

 sumed by different animals in a given time. 



When uric acid is subjected to the action 

 of oxygen, it is first resolved, as is well 

 known, into alloxan and urea. (32.) A new 

 supply of oxygen acting on the alloxan 

 causes it to resolve itself either into oxalic 

 acid and urea, into oxaluric and parabanic 

 acids, (33,) or into carbonic acid and urea. 



32. In the so-called mulberry calculi we 

 find oxalate of lime, in other calculi urate 

 of ammonia, and always in persons, in 

 whom, from want of exercise and labour, 

 or from other causes, the supply of oxygen 

 has been diminished. Calculi containing 

 uric acid or oxalic acid are never found in 

 phthisical patients ; and it is a common 

 occurrence in France, among patients suf- 

 fering from calculous complaints, that when 

 they go to the country^ where they take 

 more exercise, the compounds of uric acid, 

 which were deposited in the bladder during 

 their residence in town, are succeeded by 

 oxalates (mulberry calculus,) in consequence 

 of the increased supply of oxygen. With 

 a still greater supply of oxygen they would 

 have yielded, in healthy subjects, only the 

 last product of the oxidation of uric acid, 

 namely, carbonic acid and urea. 



An erroneous interpretation of the unde- 

 niable fact that all substances incapable of 

 farther use in the organism are separated by 

 the kidneys and expelled from the body in 

 the urine, altered or unaltered, has led prac- 

 tical medical men to the idea, that the food, 

 and especially nitrogenized food, may have 

 a direct influence on the formation of urinary 

 calculi. There are no reasons which sup- 

 port this opinion, while those opposed to it 

 are innumerable. It is possible that there 

 may be taken, in the food, a number of mat- 

 teis changed by the culinary art, which, as 

 oeing no longer adapted to the formation of 

 blood, are expelled in the urine, more or 

 less altered by the respiratory process. But 

 roasting and boiling alter in no way the 

 composition of animal food. (34.) 



Boiled and roasted flesh is converted at 

 once into blood ; while the uric acid and 

 urea are derived from the metamorphosed 



tissues. The quantity of these products 

 increases with the rapidity of transformation 

 in a given time, but bears no proportion to 

 the amount of food taken in the same period. 

 In a starving man who is in any way com- 

 pelled to undergo severe and continued ex- 

 ertion, more urea is secreted than in the 

 most highly fed individual, if in a state of 

 rest. In fevers and during rapid emaciation 

 the urine contains more urea than in a state 

 of health. (Prout.) 



33. In the same way, therefore, as the 

 hippuric acid, present m the urine of the 

 horse when at rest, is converted into ben- 

 zoate of ammonia and carbonic acid as soon 

 as the animal is compelled to labour, so the 

 uric acid disappears in the urine of man, 

 when he receives, through the skin and 

 lungs, a quantity of oxygen sufficient to 

 oxidize the products of the transformation 

 of the tissues. The use of wine and fat, 

 which are only so far altered in the organ- 

 ism that they combine with oxygen, has a 

 marked influence on the formation of uric 

 acid. The urine, after fat food has been 

 taken, is turbid, and deposits minute crystals 

 of uric acid. (Prout.) The same thing is 

 observed after the use of wines in which 

 the alkali necessary to retain the uric acid 

 in solution is wanting, but never from the 

 use of Rhenish wines, which contain so 

 much tartar. 



In animals which drink much water, by 

 means of which the sparingly soluble uric 

 acid is kept dissolved, so that the inspired 

 oxygen can act on it, no uric acid is found 

 in the urine, but only urea. In birds, which 

 seldom drink, uric acid predominates. 



If to one atom of uric acid we add 6 atoms 

 of oxygen and 4 atoms of water, it resolves 

 itself into urea and carbonic acid: 

 1 atom uric acid 

 4 atoms water > 

 6 atoms oxygen $" 



.H 4 O 10 



f 2 atoms urea 



I 6 atoms carbonic acid 



C 4 N 4 H 8 0* 

 C 6 O" 



C 10 N 4 H 8 O 16 



34. The urine of the herbivora contains no 

 uric acid, but ammonia, urea, and hippuric 

 or benzoic acid. By the addition of 9 atoms 

 of oxygen to the empirical formula of their 

 blood multiplied by 5, we obtain the ele- 

 ments of 6 at. of hippuric acid, 9 at. of 

 urea, 3 at. of choleic acid, 3 at. of water, 

 and 3 at. of ammonia; or, if we suppose 

 45 atoms of oxygen to be added to the blood 

 during its metamorphoses, then we obtain 

 6 at. of benzoic acid, 13 at. of urea, 3 at 

 of choleic acid, 15 at. of carbonic acid, and 

 12 at. of water. 



5(C 48 N 6 H 39 O ls )-f O 9 



("6 atoms hippuric acid, 6 

 9 atoms urea ... 9 

 6 atoms choleic acid . 3 

 3 atoms ammonia . 3 

 3 atoms water . 3 



C 18 N H 8 O 5 ) = C !08 N 6 H^O 30 



Q2 N 2 H 4 Q 2 ) = C 18 N^H^O 18 



H 38 O") = C 114 N 3 H^O 33 . 

 N H 3 ) = N 3 H 9 

 H 3 O 3 ) = H 3 O 3 



