88 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



relation of Hippuric to Benzoic acid is further indicated by the well-established 

 fact, that not only benzoic acid, but also the oil of bitter almonds, and cinnamic 

 acid, which have the same compound radical benzoi/l, are converted into hippuric 

 acid in the body. 1 



59. The remarkable predominance of Carbon in Hippuric acid, and its limita- 

 tion to the urine of animals which partly or entirely subsist on vegetable food, 

 seem at first sight to support the idea of its discoverer, that it is mainly formed 

 at the expense of the non-azotized articles of food. But this view is directly op- 

 posed by the following facts stated by Prof. Lehmann : In the urine of patients 

 suffering under febrile diseases, and taking but a very small amount of food of 

 any kind, the amount of hippuric acid in the urine is increased ; the urine of 

 tortoises which had been kept fasting for more than six weeks, still contained 

 hippuric acid; and the urine of diabetic patients restricted to a purely animal 

 diet also exhibits it. Further, it is occasionally to be detected, as we learn 

 from Dr. G. Bird (op. cit. p. 195), in the urine of infants at the breast. More- 

 over, since it has been ascertained by Guckelberger that the azotized histogenetic 

 substances, when treated with oxidizing agents, yield benzoyl-compounds ; and 

 since albuminous as well as gelatinous substances yield glycine ( 33); it would 

 appear highly probable that Hippuric acid is to be regarded as one of the products 

 of their decomposition, and that it is not in any way derived from non-azotized 

 articles of food. The peculiar richness in carbon which distinguishes this sub- 

 stance is by no means opposed to such a view ; since an equal proportion is found 

 in biliary matters, and also in the coloring matters of the urine, the materials 

 of both of which are unquestionably derived in great part from the metamorphosis 

 of the azotized tissues. And when all the facts of the case are taken into account, 

 it does not seem difficult to account for the peculiar proneness of this acid to 

 appear in the urine of herbivorous animals; since the abundance of the carbona- 

 ceous elements of their food will tend to prevent the oxidation of the highly- 

 carbonized products of the waste of the tissues, and will thus leave these to be 

 got rid of through the liver and kidneys. And this view derives confirmation 

 from the fact, that when stall-fed animals, in whose urine hippuric acid abounds, 

 are subjected to exercise, the hippuric acid is more or less completely replaced 

 by benzoic acid which contains a smaller proportion of carbon. Further, when 

 hippuric acid presents itself in unusual amount in states of disease, its appearance 

 is generally coincident with imperfect action, either of the lungs, skin, or liver, 

 which are the three great emunctories of carbonaceous matters; so that its pre- 

 sence in the urine may be considered as indicating that a larger amount of car- 

 bonaceous matter is present in the circulation, than the respiratory process, with 

 the cutaneous and biliary excretions, can remove. That there is generally a 

 deficiency of urea in the urine, when hippuric acid makes its appearance in un- 

 usual quantity, seems an additional indication that these two substances are 

 derived from the same ultimate sources. Hippuric acid has not yet been detected 

 in Human blood, or in any other secretion than the urinary ; but it has been 

 discovered in the blood of the Ox. 



6j). Two substances have been recently detected in the urine, which are of 

 very considerable interest, as tending to connect the formation of the components 

 of this secretion with the disintegration of the azotized tissues, more intimately 



1 It was at one time considered, that the hippuric acid which appears in the urine after 

 the administration of the benzoic, is formed at the expense of the uric ; and it was proposed 

 by Dr. A. Ure to administer benzoic acid, when a tendency to the increased production or 

 to the precipitation of uric acid shows itself in the system, in order that it may be eliminated 

 in the more soluble form of hippuric acid. But the results of analysis do not bear out this 

 view ; the quantity of uric acid in the urine, after the administration of benzoic acid, not 

 showing any perceptible diminution. 



