ELEMENTS OF COMPOSITION. 



39 



Fig. 17. Crystals of benzoic acid. 



The same effect is produced by animal ferments in the presence of 

 alkalies (Buchner). 



Like the acids we have just been considering, hippuric is nowhere 

 found in the vegetable kingdom. It is doubtful whether it exists in the 

 blood of vegetable-feeding mammals and that of man (Robin and Verdeil). 

 It appears in human urine in about the 

 same quantity as uric acid, though in 

 larger amount in certain diseased states 

 of the system. The proportion of hip- 

 puric acid in the urine of phytophagous 

 animals is greater, as, for instance, in 

 that of the horse. Up to the present 

 this acid has not been met with in the 

 juices of the organism ; it has, however, 

 been found in the scales of a skin disease 

 known as ichthyosis. 



It is a fact of great interest, that ben- 

 zoic, kinic, and cinnamic acids, oil of 

 bitter almonds, and of tolu, introduced into the stomach, are excreted as 

 hippuric acid through the kidneys. 



Hippuric acid possesses the nature of a decomposition product of 

 azotised substances of the body. The fact that on the oxidation of pro- 

 tein substances by permanganate of potash, a great quantity of benzoic 

 acid is developed, is in favour of this view. 



27. 

 Glycocholic Acid, C., 6 H 48 N0 6 . 



This, which belongs to the bile, is of analogous constitution to hippuric 

 acid, splitting up like the latter into glycin and a non-nitrogenous acid, 

 known as cholic acid. 



Let us consider this latter in the first place : 



Cholic, or cholalic acid of Strecker, C 24 H 40 5 , crystallizes from ether 

 with two equivalents of water of crystallization in rhombic tables ; from 

 alcohol with five molecules of water in tetrahedrons : or more rarely, in 

 square octahedrons, which effloresce when exposed to the air. This acid 

 is insoluble in water, but very soluble in alcohol and ether. "With 

 sulphuric acid and sugar it becomes of a purple-violet colour. The con- 

 stitution and origin of cholic acid has not 

 been fixed as yet. 



Let us now return to glycocholic acid. 

 This crystallizes in very fine needles, which 

 maybe heated to 130 C. without under- 

 going change. It is tolerably soluble in 

 water, very easily so in alcohol and alkalies, 

 but insoluble in ether. It may also be 

 dissolved cold, and without decomposition, 

 in many mineral acids, as, for instance, Fig. m Crystals of cholic acid, 

 sulphuric and hydrochloric, but also in acetic acid. With sugar and 

 sulphuric acid it gives the reactions of cholic acid. It is , monobasic, 

 and forms partly crystalline, partly amorphous salts, soluble in spirits 

 of wine. 



On being boiled with potash ley or baryta water it is split up with 



