SECRETION OF URTNE. 537 



Muriates find their way into the Urine is easily understood. Of the Common 

 Salt ingested, a considerable part is decomposed into Muriatic Acid and Soda; 

 the former being found uncombined in the Gastric juice ; and the latter in the 

 Bile. By the mixture of the Bile with the Chyme, a re-union of these two 

 constituents takes place ; and Salt is again formed, which is received into the 

 Circulation, that it may be eliminated its part in the economy having been 

 now performed by the Kidney. The quantity of the Sulphates present in 

 the Urine appears to have no relation with that of the amount of Sulphuric 

 acid ingested; for it much surpasses what could be thus accounted for, being 

 often considerable when no Sulphate whatever can be detected in the food. 

 But most of the azotized compounds employed as food have Sulphur in com- 

 bination with them ; and there can be no doubt, that this undergoes oxidation 

 within the system and thus generates Sulphuric acid, which unites with any 

 free or weakly-combined bases it may meet with, to form the Sulphates 

 present in the Urine. The Phosphates are probably derived in part from the 

 Phosphates taken in with the food, and in part from the free Phosphorus, 

 which its elements contain. Of the latter, great use is made, in the produc- 

 tion of Nervous matter ( 643) : the continual waste of which must set it free 

 again. When thus set free, there is obviously no channel for its elimination, 

 save by its conversion into Phosphoric acid, and its union with an alkaline 

 base.* That this is really the case, would appear from the fact noticed by 

 Dr. Prout, and confirmed by many others, that mental or bodily labour, 

 which involves much waste of the Nervous System, is followed by an increase 

 in the quantity of the Phosphates in the Urine. This increase cannot pro- 

 ceed from the waste of the Muscular system ; for this would set free Phosphate 

 of Lime, which passes off by the faeces. 



678. The alkaline or acid reaction of the Urine, therefore, will not only 

 depend upon the quantity of alkaline Phosphates converted into acid Phos- 

 phates by the Uric and Hippuric acids ( 673) ; but also upon the amount of 

 the bases in the ingesta, compared with that of the permanent Acids intro- 

 duced into the system or generated within it. The Urine of animals which 

 live chiefly or entirely upon Vegetable food, is almost invariably alkaline; 

 because this food contains a large quantity of alkaline bases, in combination 

 with Citric, Tartaric, Oxalic, and other acids, which are decomposed within 

 the system ; and the amount of Sulphuric and Phosphoric acids produced is 

 not sufficient to neutralize them. On the other hand, the food of Carnivorous 

 animals contains no free or weakly combined basis ; and as its Sulphur and 

 Phosphorus, when oxidized in the system, produce a considerable quantity of 

 free acids, which share the bases with the Muriatic acid already there, the 

 Urine must necessarily have an acid reaction. The character of the Urine of 

 Man, in this respect, is considered by Liebig to depend entirely upon that of 

 the food ingested. t 



* This circumstance has been entirely overlooked by Liebig, in his late discussion 

 (loc. czV.) of the Constitution of the Urine ; the Phosphates being regarded by him as hav- 

 ing their sole origin in the Phosphates of the ingesta. 



j- Proceeding upon his assumption (borne out certainly by the results of his own ex- 

 periments, but not to be received until these experiments have been repeated in a greater 

 variety of modes) that no Lactic acid is ever present in the Urine, he remarks : "The 

 acid, neutral, or alkaline reaction of Urine of healthy individuals does not depend on any 

 difference in the processes of digestion, respiration, or secretion, in the various classes 

 of animals, but upon the constitution of the aliments, and upon the alkaline bases which 

 enter the organism through the medium of these aliments. If the amount of these bases 

 is sufficiently large to neutralize the acids formed in the organism, or supplied by the 

 aliments, the urine is neutral ; whilst it manifests an alkaline reaction, when the amount 

 of alkaline bases thus supplied to the organism is more than sufficient to neutralize the 

 acids; but in all these cases, the urine accords with the nature of the aliments taken." 

 The varying amount of Uric Acid, which, on Prof. Liebig's own showing, is very much 



