326 APPENDIX. 



acid with his food, an acid crystallizing in needle-shaped 

 prisms, which had the general properties of benzoic acid, 

 and which he then took for benzoic acid. (Tiedemann's 

 Zeitschrift fur Physiologic, i. 142.) These crystals were 

 obviously hippuric acid, as plainly appears from the 

 statements, that they had the aspect of nitre, and, when 

 sublimed, left a residue of carbon. But at that time hip- 

 puric acid was not yet discovered ; and it is well known, 

 that till 1829, when these acids were first distinguished 

 from each other by Liebig, it was uniformly confounded 

 with benzoic acid. 



The recently published statement of A. Ure, that he 

 actually found hippuric acid in the urine of a patient who 

 had taken benzoic acid, recalled this relation, so remark- 

 able in a physiological point of view, and induced me to 

 undertake the following experiments, which, at the sug- 

 gestion of Professor Wohler, I made on myself. The sup- 

 posed conversion of benzoic acid into hippuric acid has, 

 by these experiments, been unequivocally established. 



I took, in the evening before bedtime, about thirty- 

 two grains of pure benzoic acid in syrup. During the 

 night I perspired strongly, which was probably an effect 

 of the acid, as in general I am with great difficulty made 

 to transpire profusely. I could perceive no other effect, 

 even when, next day, I took the same dose three times ; 

 indeed, even the perspiration did not again occur. 



The urine passed in the morning had an uncommonly 

 strong acid reaction, even after it had been evaporated, 

 and had stood for twelve hours. It deposited only the 

 usual sediment of earthy salts. But when it was mixed 

 with muriatic acid, and allowed to stand, there were 

 formed in it long prismatic, brownish crystals, in great 

 quantity, which, even in this state, could not be taken for 

 benzoic acid. Another portion, evaporated to the con- 



