CONVERSION OF BENZOIC INTO HIPPURIC ACID. 9 
cause benzoic acid is converted into hippuric by entering 
into the system, it should, therefore, necessarily affect the 
usual chemical changes in the body. We are disposed to 
consider it as a mere chemical reaction between the benzoic 
acid and the substances of the blood, either those which 
are used for the formation of the tissues, or, more proba- 
bly, those which result from their dissolution. But if this 
be correct, it follows, that we may be able to perform the 
same transformation out of the body. It was with a view 
of determining this point that our experiments were under- 
taken, and we still look for success, although they have not 
hitherto afforded a satisfactory result. 
Woehler was the first to observe that benzoic acid, when 
administered internally to a dog, and again separated from 
the urine, reappeared as prismatic crystals, unlike benzoic 
acid; and he conjectured correctly, from their resemblance 
to hippuric acid, that the former by passing through the 
system was converted into the latter. He also suggested, 
that this might be the source of *the hippuric acid in the 
urine of herbivorous animals, since the benzoic acid might 
be supposed to occur in their food, and by the digestion be 
converted into hippuric. Ure subsequently stated, that he 
had found hippuric acid in the urine of a patient who had 
taken benzoic acid ;he also supposed that the uric acid had 
been employed in this conversion, and recommended it as 
a remedy for calculous concretions of uric or lithic acid. 
This induced Keller, at the instigation of Woehler, to make 
some experiments on this point, which he published in Lie- 
big's Annals of Chemistry and Pharmacy. He took, in 
the evening before bed-time, two grammes or about thirty- 
one grains of benzoic acid, and found the next morning, on 
examining the urine, that by the addition of chlorohydric 
acid it deposited long prismatic crystals, which it continued 
to do as long as he continued the use of benzoic acid. By 
re-dissolving these crystals in hot water and treating them 
with animal charcoal, he obtained them perfectly colour- 
