198 CONJUGATED ACIDS. 



almonds, and cinriamic acid, which is very similar to benzoic acid, 

 are transformed in the animal body into hippuric acid. Now, since 

 the benzoyl-compounds are almost entirely confined to the vege- 

 table kingdom, we might believe that this constituent of hippuric 

 acid principally arises from vegetable food, and the abundance 

 of this acid in the urine of many herbivorous animals is in favour 

 of this view. We might therefore be led to regard one constituent 

 of hippuric acid as an immediate product of decomposition of 

 certain constituents of food, namely, of the vegetable portion ; but 

 this view is opposed by several positive experimental results ; thus 

 in the urine of patients on an antiphlogistic diet, who for several 

 days have scarcely taken any food, the amount of hippuric acid is 

 actually increased. 



The urine of tortoises, which had been kept fasting for more 

 than six weeks, still contained hippuric acid ; and it occurred in 

 the urine of diabetic patients who were restricted to a purely 

 animal diet. In the urine of granivorous birds, as well as in that 

 of the larva of Sphinx Cossus, and of several other herbivorous 

 insects, I have found, after careful examination, larger or smaller 

 quantities of uric acid, but no hippuric acid. Hence we may con- 

 clude in the first place that the formation of uric acid is not depen- 

 dent on the use of animal food; or that of hippuric acid on the use 

 of vegetable food, and secondly, that the latter acid must derive its 

 nitrogenous constituent from the retrograde metamorphosis of the 

 animal tissues. This is, moreover, not opposed to our chemical 

 facts in relation to the production of the benzoyl-compounds, for 

 there is every reason to believe that the nitrogenous tissues which, 

 according to the admirable investigations of Guckelberger, when 

 treated with oxidising agents, yield benzoic acid and benzonitrile, 

 yield a like product of decomposition during the gradual oxidation 

 which they undergo in the animal body. 



In reference to the nitrogenous constituent of hippuric acid we 

 may regard it as fumaramide, or as glycine; it is undoubtedly 

 derived from the animal albuminous substances, and probably 

 from effete tissue. It would, however, certainly be rash to attri- 

 bute it principally to the decomposition of the gelatigenous tissues, 

 simply because it is chiefly formed from them in artificial experi- 

 ments ; but independently of the circumstance that this product 

 into which the nitrogenous adjunct of hippuric acid becomes con- 

 verted, may also be obtained from albuminous substances, we 

 must bear in mind that the metamorphosis going on in the gelati- 

 genous tissues is certainly too insignificant to account for the 



