ON THE FORMATION OF SEDIMENTS. 407 



before the deposition of the precipitate of urate of soda. The 

 analysis of the urine shows, moreover, as Becquerel specially- 

 noticed, that a non-sedimentary urine very often contains a much 

 larger quantity of urates than a sedimentary one. The separation 

 of urate of soda must, therefore, depend upon some other cause 

 than on the mere decrease of the temperature of the urine. The 

 simplest induction leads us to assume that some alteration must 

 occur in the urine when it is exposed to the atmosphere, which 

 it does not experience within the bladder, and which is independent 

 of a mere diminution of temperature. This alteration must, therefore, 

 originate in some metamorphic process effected by the atmosphere 

 in one or other of the constituents of the urine. The following 

 facts induce us to regard the coloured extractive matter, or the 

 extractive pigment of the urine as the substance which causes a 

 large quantity of the urate of soda in the urine to remain in a state 

 of solution, and which by its metamorphosis gives rise to the 

 separation of a large portion of this urate. We know that this 

 colouring extractive matter combines especially with the urates, 

 whose properties it essentially modifies. I have elsewhere* shown 

 that it is this extractive substance which hinders the urate of soda, 

 when a warm solution is suffered to cool, from separating into the 

 well-known groups of crystals ; for if we add to a solution oF 

 urate of soda, which had deposited beautiful colourless bundles of 

 crystals on cooling, some of the extractive matter of the urine 

 which is soluble in alcohol, this salt loses its capacity for crystal- 

 lization, and the same corpuscles are deposited in the cooling 

 solution, which are generally found, although not in a crystalline 

 form, to be separated from the urine, and which, moreover, occur 

 in a smaller quantity, as may be seen by the naked eye, indepen- 

 dently of weighing. Any one, moreover, who has collected on a 

 filter this spontaneous urinary sediment, must have noticed that 

 the metamorphosis of the pigment exerts a direct influence on the 

 entire constitution of the urate of soda. On examining the deposit 

 upon the filter, the bright red or even scarlet colour assumed by 

 the sediment strikes the observer very forcibly ; but on examining 

 it more attentively, either through the microscope, or after we have 

 attempted to dissolve it in hot water and to filter it, a number of the 

 most beautiful crystals of uric acid will appear, of which not a trace 

 can be discovered in the portion of the urine which was not filtered, 

 and whose sediment, from not having been exposed to the action 



* Gosehen's Jahresber. 1JJ44. - Bd. 2,.S. 26,^ 



