36 Dr. Venables on the Cystic Oxide, &c. 



have enjoyed tlie most extensive opportunities of observation. 

 The almost total absence of Hthic acid prevents the possibility 

 of any contamination with this principle or its compounds, 

 while the tendency in the urine to alkalescence during the pre- 

 valence of the cystic oxide diathesis, would be unfavourable to 

 the separation of the lithic acid, even if it existed in larger 

 quantity. The absence of urea removes one source of the 

 formation of alkali in the urine, and of course the precipitation 

 of the phosphates. Urea, especially in mucous, and several 

 other disordered states of the urine, speedily undergoes decom- 

 position, evolving ammonia or its carbonate 3 hence the excess 

 of phosphoric acid in the superphosphates of ammonia and of 

 magnesia, &c., by which the latter is held in solution, 

 being neutralized, the triple salt precipitates. But as the urea 

 is so deficient in this diathesis, it is evident a very powerfully 

 operative source of contamination with the phosphates is sup- 

 pressed. 



The faintly acidulous reaction noticed in tjiis urine was 

 owing unquestionably to the superphosphates of ammonia, 

 magnesia, &c. ; and it must be observed that the excess of 

 acid in super-salts is in a very different state from that of a 

 free acid; for although in excess as it is termed, it is still in 

 combination, and so long as the combination exists, incapable 

 of exerting the full chemical reagencies of a free or uncombined 

 acid. It is upon these principles that we may explain the fact 

 of the comparatively large proportion of the cystic oxide in 

 mechanical suspension, and the small quantity of the same 

 principle in actual solution. Probably the affinities of the 

 oxide and excess of phosphoric acid for each other were infe- 

 rior to those of this excess for the alkaline bases with which 

 it was combined. Or, to speak more chemically, " the sum 

 of the quiescent exceeded that of the divellent affinities,'* 

 and consequently the intregrity of the super-salts was pre- 

 served. 



Hence, too, we can explain the readiness with which the 

 cystic oxide, when abundantly secreted, separates, as already 

 observed, from the urine in the kidney, and concretes into cal- 

 culous masses before reaching the bladder. When the specific 

 gravity of the urine is high, and the quantity of cystic oxide 

 secreted not superabundant — and this principle, even when 



