ACID FERMENTATION OF THE URINE. 359 



and communicates these alterations more or less rapidly to the super- 

 natant fluid. The first of these changes is called the acid fermenta- 

 tion of the urine. It consists in the production of a free acid, usually 

 lactic acid, from some of the undetermined animal matters con- 

 tained in the excretion. This fermentation takes place very early ; 

 within the first twelve, twenty-four, or forty-eight hours, according 

 to the elevation of the surrounding temperature. Perfectly fresh 

 urine, as we have already stated, contains no free acid, its acid 

 reaction with test paper being dependent entirely on the presence 

 of biphosphate of soda. Lactic acid nevertheless has been so fre- 

 quently found in nearly fresh urine as to lead some eminent 

 chemists (Berzelius, Lehmann) to regard it as a natural constituent 

 of the excretion. It has been subsequently found, however, that 

 urine, though entirely free from lactic acid when first passed, may 

 frequently present traces of this substance after some hours' expo- 

 sure to the air. The lactic acid is undoubtedly formed, in these 

 cases, by the decomposition of some animal substance contained in 

 the urine. Its production in this way, though not constant, seems 

 to be sufficiently frequent to be regarded as a normal process. 



In consequence of the presence of this acid, the urates are par- 

 tially decomposed ; and a crystalline deposit of free uric acid slowly 

 takes place, in the same manner as if a little nitric or muriatic acid 

 had been artificially mixed with the urine. It is for this reason 

 that urine which is abundant in the urates frequently shows a de- 

 posit of crystallized uric acid some hours after it has been passed, 

 though it may have been perfectly free from deposit at the time 

 of its emission. 



During the period of the " acid fermentation," there is reason to 

 believe that oxalip acid is also sometimes produced, in a similar 

 manner with the lactic. It is very certain that the deposit of oxa- 

 late of lime, far from \>eing a dangerous or even morbid symptom, 

 as it was at one time regarded, is frequently present in perfectly 

 normal urine after a day or two of exposure to the atmosphere. 

 We have often observed it, under these circumstances, when no 

 morbid symptom could be detected in connection either with the 

 kidneys or with any other bodily organ. Now, whenever oxalic 

 acid is formed in the urine, it must necessarily be deposited under 

 the form of oxalate of lime ; since this salt is entirely insoluble 

 both in water and in the urine, even when heated to the boiling 

 point. It is difficult to understand, therefore, when oxalate of lime 

 is found as a deposit in the urine, how it can previously have been 



