THE KIDNEYS SECRETION OF URINE. 509 



sediment is favored by concentration of the liquid, which thus augments the 

 proportion of the urate to the water, and at the same time intensifies the acid 

 reaction ; and thus urine whose constituents are otherwise normal, may throw 

 down a copious deposit of this kind, merely from deficiency of water ; whilst 

 an unusual amount of uric acid may be really present without being de- 

 posited, the urine, too, exhibiting its ordinary acidity, if the proportion 

 of water be large. Thus the uric acid sediment may be regarded as depen- 

 dent upon three concurrent conditions: (1) Decrease of temperature ; (2) 

 Increased proportion of uric acid compound to the water, positively or rela- 

 tively ; (3) Increased acidity of the urine. Sometimes one condition is most 

 influential, sometimes another ; but they are all usually concerned in some 

 degree. There are many diseases, especially those of a febrile nature, in 

 which the presence of an excess of uric acid is a very marked symptom ; 

 there is often, at the same time, a reduction in the proportion of urea ; and 

 thus it would seem that, with perhaps an augmented tendency to disintegra- 

 tion of the tissues, there is an incapacity for the performance of that higher 

 process of oxidation, which is requisite for the genesis of urea; so that a 

 larger proportion of the products of the "waste" passes off in the state of 

 uric acid, as in animals whose respiration is feeble. The proportion of Hip- 

 puric Acid (C w H 8 NO 5 -fHO) present in the urine appears to be in great 

 measure dependent upon the nature of the food and upon the amount of 

 exercise. According to the researches of Weissmaun and Thudichum, it 

 amounts to between 30 and 40 grains per diem on a mixed diet. On a 

 purely animal diet, it falls to about 12 grains per diem ; whilst it rises con- 

 siderably when vegetables alone are consumed ; and its origin has been at- 

 tributed by Shepard and Meissuer 1 to the conversion at the kidney of a 

 substance existing in the cuticle of plants having the formula C U H 12 O 10 and 

 nearly allied to Kinic acid. As might be anticipated, therefore, a large 

 quantity of this acid is constantly present in the urine of Herbivora, but 

 only traces exist in that of Garni vora. Both Mack and Roussin found that 

 horses at rest pass much urea and little Hippuric acid ; but when at work, 

 the quantity of Hippuric acid equalled or exceeded that of urea, the abso- 

 lute quantity of the latter undergoing a diminution equal to the increase of 

 the Hippuric acid. As urea is one of the ultimate products of oxidation in 

 the body, whilst Hippuric acid is very imperfectly oxidized, it would seern 

 that during violent exertion the due oxidation of the secondary nitrogenous 

 compounds produced by the disintegration of the tissues is interfered with, 

 perhaps by the diversion of the oxygen to form carbonic acid, the quantity 

 of which has been shown by Dr. Ed. Smith to be so notably increased by all 

 kinds of muscular exertion ; or we may, with more probability, suppose that 

 the lungs are unable to eliminate the whole of the carbon of the disinte- 

 grated tissues in the form of C0, 2 , and that a part of the carbon is conse- 

 quently discharged by the kidneys in the form of the richly carbonized com- 

 pounds, Hippuric or Beuzoic acids. The quantity of Hippuric acid eliminated 

 can be greatly increased by the administration of Benzoic, Succiuic, Ciuna- 

 mic, or Kinic acids, or of Oil of Bitter Almonds. 2 The transformation of 

 Benzoic into Hippuric acid appears to take place at the liver, as it does not 

 occur in jaundiced patients, or in dogs in whom the ductus communis chole- 

 dochus has been tied, the Benzoic acid then passing off unchanged. The 

 process is exceedingly simple. Benzoic acid (C 14 H 6 O 4 ) + Glycin (C 4 H 5 NO 4 ) 

 producing Hippuric acid (C 18 H 9 NO 6 ) + 2HO. Kiihue and Hallwachs, 

 however, maintain that the conversion occurs in the blood, and Meissner and 



1 Centralbhitt, Nos. 43 and 44, 1866. 



2 See Matschersky, Virchow's Archiv, 1863, p. 528. 



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