502 Mr. Garrod on the Conversion 



duction of the purple colour spoken of, and which has been 

 given as a test of hippuric acid. When the crystals are dis- 

 solved in alcohol the uric acid is precipitated, and the hip- 

 puric acid crystallized from the alcoholic solution no longer 

 gives the purple colour. On collecting the uric acid from the 

 same quantity of urine, formed on successive days, the same 

 food being taken, one containing about twenty-seven grains 

 of hippuric acid, and the other none, the following results 

 were obtained: — 



From 4^ oz. of urine, when no benzoic acid had been taken, 

 uric acid 1 '07 grain. 



From 4|^ oz. of urine, after taking 30 grains of benzoic 

 acid, uric acid 0*96 grain. 



Difference in favour of first, O'll grain. 



In the second experiment also, a small loss might have oc- 

 curred from the greater washing of the crystals necessary in that 

 experiment. Now if we suppose that uric acid is decomposed 

 to afford the elements necessaiy to be added to benzoic acid 

 to form hippuric acid, we find that each equivalent of benzoic 

 acid requires the addition of C4 H(j O4 N. To obtain the 

 nitrogen, four atoms of benzoic acid would require one atom of 

 uric acid, or half a drachm of benzoic acid would require rather 

 more than ten grains of uric acid. Now the quantity of urine, 

 in the experiment without the benzoic acid, only contained 

 1'07 grain of uric acid, and yet that quantity was not mate- 

 rially diminished when twenty-eight grains of hippuric acid 

 were found in the urine. It cannot therefore be from the 

 uric acid that the hippuric acid is formed. 



If we examine the subject theoretically, it does not seem 

 probable that such a body as benzoic acid, possessing such 

 feeble afiSnities, and producing no sensible action on the body 

 when taken, should be able to break up such a stable com- 

 pound as uric acid ; to abstract from the latter the requisite 

 elements for its conversion into hippuric acid. But as hippu- 

 ric acid is really formed in the urine, from whence does it 

 obtain the necessary addition ? The quantity of urea was 

 noticed in several experiments to be deficient; could this be 

 the source ? We can find no rational formula for the explana- 

 tion of the conversion if we suppose it to be from urea alone. 

 We can, it is true, select the elements required ; but, as in the 

 last case, we should leave some compound in the system, 

 which cannot be resolved into any known compounds, as am- 

 monia, water, carbonic acid, &c., while from the ready con- 

 version of the benzoic acid into hippuric acid we should expect 

 that the change was one which could easily take place, with- 

 out the action of any unusual affinities being brought into 



