MORBID CONCRETIONS. 



As urine contains both uric acid and soda, we have no rea- 

 son to be surprised at occasionally finding urate of soda in uri- 

 nary calculi. Whenever the urine is rendered alkaline by a 

 long continued use of carbonate of soda, one would naturally ex- 

 pect that the urate of ammonia would be converted into urate of 

 soda, which being insoluble or nearly so, would be precipitated 

 in crystalline grains or in powder, and this powder, cemented by 

 the mucus of the inside of the bladder, might give origin to a 

 nucleus of urate of soda. The great rarity of such calculi 

 shows how seldom the urine is rendered alkaline by an excess of 

 soda. 



Cystic oxide calculi are very rare. As this substance, so far 

 as^we know, does not exist in urine, we cannot so readily account 

 for its appearing in the urinary organs. We might indeed 

 easily start various hypotheses to connect cystic oxide with uric 

 acid, oxaluric acid, and some other substances which either exist 

 ready formed in the urine, or make their appearance in certain 

 cases. But we refrain, because such hypotheses have very little 

 tendency to improve our knowledge. 



Uric oxide, differing from uric acid simply by containing two 

 atoms less oxygen, we have only to conceive the action of some 

 deoxygenizing principle upon uric acid in the urine, in order to 

 account for the appearance of these calculi. Carbon, for exam- 

 ple, in some state or other, might be conceived to deprive uric 

 acid of two atoms oxygen, and to be converted into carbonic acid, 

 while it left the uric acid converted into uric oxide. 



Fibrinous calculi seem always to be formed in the bladder. 

 We cannot at present account for their origin, though it may 

 be connected with the presence of albumen in urine. For it 

 has been shown in a former part of this work that albumen and 

 fibrin are mere varieties of the same animal principle. 



Urinary calculi from the inferior animals. These calculi have 

 hitherto been imperfectly examined. Indeed, if we except those 

 animals which have been domesticated, few opportunities occur 

 for examining the calculi which may be formed in the urinary 

 organs of the inferior animals. 



1. The Horse. Dr Pearson analyzed several calculi from the 

 horse. He found them to consist of phosphate of lime, phos- 

 phate of ammonia, and animal matter.* But a calculus from a 



* Phil. Trans. 1798, p. 15. 



