1867.] Ammonia in Urine. 143 



of oxalate of lime so often taking place in the secretion. The appearance 

 of oxalate of lime as a deposit from urine long after its emission has 

 hitherto been a puzzling phenomenon, and the most improbable hypotheses 

 have been resorted to in order to explain it. It has, for instance, been 

 assumed that there exists in the animal economy a tendency to the forma- 

 tion of a soluble triple compound of oxalic acid, lime, and albumen, which, 

 by its decomposition, allows oxalate of lime to crystallize. Then it has 

 been maintained by Rees that uric acid and the urates furnish oxalic acid 

 when the urine containing them is sim.ply heated or boiled ; though this 

 statement is questioned by other observers, and it is certain that under 

 ordinary ch'cumstances the conversion of one into the other can only be 

 effected by means of very powerful oxidizing agents such as nitric acid. 

 The attempts which have been made to prove that oxalate of lime may 

 exist ready formed and in a state of solution in the urine are also unsatis- 

 factory, the only known solvent likely to occur naturally being acid phos- 

 phate of soda. Were this salt really the means of keeping the oxalate 

 dissolved, the latter would only be deposited v/hen the acid reaction of the 

 urine had disappeared, or had at least somewhat diminished, which is not 

 the case. Now, however, the whole process may be easily explained. 

 Oxaluric acid, as all chemists know, may be considered as a compound of 

 oxalic acid and urea minus water, its composition corresponding to that of 

 oxamic acid. By the action of acids, alkalies, or even water at a high 

 temperature, it is decomposed, yielding oxalic acid and urea. How easily 

 this process of decomposition may be set up in urine when allowed to 

 stand, or even boiled, need not be pointed out. The oxalic acid as soon as 

 formed combines, of*course, with the lime which is always present in urine, 

 producing the well-known deposit of oxalate. Those who maintain, with 

 Rees, that oxalate of lime may be produced in the urine after excretion are 

 therefore quite correct, though the phenomenon has hitherto been wrongly 

 interpreted. The conversion of oxaluric into oxalic acid may, however, 

 commence alreadj in the bladder, or even more remote parts of the system, 

 and thus lead to the formation of concretions and calculi. Regardino; tlie 

 origin of the oxaluric acid of urine there can be little doubt. In the animal 

 frame, just as in the laboratory, it must be formed by the oxidation of uric 

 acid, which is its only known source ; it may be considered as the vehicle ap- 

 pointed by nature for getting rid of oxalic acid in the least injurious form. 

 Were this acid excreted as such, it v/ould, by combining with lime, produce 

 serious results, which are prevented by the simple expedient of causing it to 

 pass off in a state of intimate union with urea. 



