ITS INCIDENTAL CONSTITUENTS. 417 



that cinnamic ' acid, C 18 H 7 O 3 . HO, in its passage through the 

 animal organism assimilates nitrogenous matter, and escapes in 

 the urine as hippuric acid. 



There are various ways in which we may suppose that the con- 

 version of cinnamic into hippuric acid may take place : it may 

 either lose four atoms of carbon and two atoms of hydrogen, in 

 order to be first converted into benzoic acid (for C 18 H 7 O 3 

 [4 C + 2 H] = C 14 H 5 O 3 ), or by the assimilation of ammonia and 

 the separation of water there is formed cinnamide (C 18 H 7 O 3 + H 3 N 

 HO = C 18 H 9 NO 2 ), which has only to take up four atoms of 

 oxygen in order to form water and hippuric acid (C 18 H 9 NO. 2 + 

 4 O=3 HO + C 18 H 8 NO 5 . HO). 



It is worthy of notice that cummic acid, which is so closely 

 allied to benzoic acid, does not resemble benzoic and cinnamic 

 acids, in combining with nitrogenous matter within the animal or- 

 ganism, but passes unchanged into the urine; hence in its behaviour 

 it resembles salicylous acid (hydride of salicyl) which is even more 

 nearly allied to benzoic acid. 



Wohler and Frerichs have convinced themselves by experi- 

 ments on several rabbits and dogs, that uric acid, whether intro- 

 duced into the stomach or injected into the veins, is decomposed 

 in the animal body in precisely the same manner as by peroxide 

 of lead ; the urine is at all events found to be far richer in urea 

 and oxalate of lime after the administration of the acid. 



We are indebted to Wohler for one of the most important 

 discoveries in physiological chemistry, namely, that the neutral 

 salts formed by the combination of the alkalies with vegetable 

 acids, are oxidised in the animal organism in precisely the 

 same manner as if they were burned in oxygen gas: alkaline 

 carbonates pass into the urine and render it alkaline ; it 

 consequently becomes turbid from the separation of earthy phos- 

 phates, and naturally effervesces with acids. That the conversion 

 of the alkaline salts of the organic acids into carbonates takes 

 place in the blood, might have been a priori con eluded; but I have 

 convinced myself, by the injection of an alkaline lactate into the 

 jugular vein of dogs, that the change takes place with extraordi- 

 nary rapidity, and that an alkaline carbonate very soon appears 

 in the urine (see vol. i., p. 97). The same experiment has 

 been made by others. It is, however, a singular circumstance, 

 and one that requires further investigation, that in different 

 persons, even under, apparently, precisely similar conditions, the 

 period that elapses before the urine becomes alkaline, after the 



VOL. II. 2 E 



