8 CONVERSION OF BENZOIC INTO HIPPURIC ACID. 
more probable to suppose that it takes place during the 
subsequent circulation of the blood, and that its formation 
is connected with that of the urea. We know that at least 
the principal source of urea is the transformation of the 
tissues in the body, or what Prout calls the destructive as- 
similation, since its formation continues, when animals are 
fed exclusively on non-nitrogenized food, and when they 
are starved ; and that it is not secreted by the kidneys, but 
actually formed in the body, and merely excreted by them, 
is proved by removing them, when urea will be found in 
the blood. The same occurs by suppression of urine. I 
have myself lately had an opportunity to confirm this ob- 
servation, in examining, at the request of Drs. Pepper and 
Sargent, the blood of a patient who for some time previous 
to her death had a complete suppression of the urine. But 
the question then is, — is it merely a simple chemical reac- 
tion between the benzoic acid and the products of the trans- 
formations of the tissues, or does it actually affect the che- 
mical changes, by which the latter are effected, so as to 
cause new chemical products to be their results. Liebig 
takes this latter view in his Animal Chemistry. We quote 
his own words : 
" Benzoic acid, when administered internally, appears in 
the form of hippuric acid. Should the observation be con- 
firmed, it will acquire great physiological significance, since 
it would plainly prove, that the act of the transformation 
of the tissues in the animal body under the influence of 
certain matters taken in the food, assumes a new form with 
respect to the products, which are its results ; for hippuric 
acid contains the elements of one at. of urea, one of lactic 
acid, and two of benzoic acid/' 
Liebig then at once proceeds to make an application of 
this fact to the action of medicinal agents. We are not 
disposed to dispute his theories on this point, nor deny that 
such may be the case in active remedies, but we believe 
that he is too prompt in drawing the conclusion, that be- 
