780 SPECIAL PHYSIOLOGY. 



be detected in the blood. The gouty concretions, known as chalk- 

 stones, are composed of urate of soda, with traces of urate of lime. 

 When, in acute inflammatory disease, the uric acid is increased, the 

 urea is simultaneously diminished. In diseases of debility, this acid is 

 usually diminished in quantity ; it may also be reduced by a spare diet, 

 the avoidance of acids, the use of large quantities of water, open-air 

 exercise, so as to insure the perfect oxygenation of the blood, and by 

 all measures tending to increase the action of the skin, such as exer- 

 tion, friction, baths, especially hot-air and water baths, and warm cli- 

 mates. The use of tobacco augments its excretion, whilst quinine and 

 alcohol lessen it. Alkalies assist in its excretion. 



Hippuric acid (fmcos, a horse), first detected in the urine of the 

 horse, is also constantly present in human urine, sometimes amounting 

 to as much as 15 grains in twenty-four hours ; it has often been over- 

 looked. (Liebig.) It crystallizes in four-sided prisms, and has the 

 atomic composition, C 9 H 9 N0 3 , so that it is neither so nitrogenous nor 

 so completely an oxidized body as urea or uric acid, but contains a 

 larger proportion of carbon than either substance. Ben zoic acid and 

 other benzoyl compounds, also oil of bitter almonds, and succinic and 

 other allied acids, when taken internally, cause an excess of hippuric 

 acid in the urine (lire). To explain this, it has been suggested that 

 benzoic acid, C 7 H 6 2 , combined with the bile product, glycocoll, 

 C 2 H 5 N0 2 , is equal to one atom of hippuric acid, and one atom of water. 

 The source of the hippuric acid ordinarily present is not yet known. 

 Its quantity is influenced by the character of the diet, and by the 

 amount of exercise; it is increased by a purely vegetable diet, is 

 lessened by a mixed diet, and is diminished still more remarkably in 

 those who are living on animal food only. According to some, it is 

 absent in persons who abstain from spices; also in infants at the 

 breast, and in Herbivorous animals deprived of food. In the last two 

 cases, uric acid alone is produced, in the one case, from the milk, and 

 in the other, from the tissues of the animal itself. (Ranke.) Hippuric 

 acid is not only found in large quantities in the horse, but also in 

 other Herbivorous animals ; and most of these consume grasses, in 

 many species of which certain aromatic principles exist. In the 

 Carnivora, it exists in minute quantities. Although, most probably, 

 hippuric acid is commonly derived from certain aromatic substances, 

 yet it has been shown that its formation from albuminoid bodies is 

 quite possible. (Stadeler.) 



Very minute quantities of benzoic acid, and xanthin or xanthic 

 oxide, also exist in the urine, with traces of certain volatile acids, 

 phenylic, carbolic, and taurilic, on which the odor of this fluid may 

 depend. 



The creatin and ereatinin found in the urine, are both crystallizable 

 nitrogenous bodies. The former exists in small quantities, the latter 

 amounts to about 15 grains a day. Creatinin C 4 H 7 N 3 0-f-2(HO), dif- 

 fers from creatin C 4 H 9 K 3 2 by one atom of water. They are obtained 

 by precipitation with salts of zinc, and by the subsequent decomposi- 

 tion of the zinc compounds. Creatin is a neutral substance, incapable 

 of combining either with acids or alkalies ; but ereatinin is a powerful 



