60 DISEASES OF THE PELVIS OF THE KIDNEYS AND URETERS. 



gravel), or form masses varying in size from that of a mustard-seed 

 to that of the fist. They are classified, according to their composition, 

 into 1. Those composed of pure uric acid, or of uric-acid salts ; 

 2. Those composed of oxalate of lime ; 3. Stones of phosphate of 

 magnesia and ammonia and phosphate of lime ; 4. Stones of car- 

 bonate of lime ; 5. Cystine calculi ; 6. Xanthine stones. Besides 

 these, there are stones of several components, which are often so 

 formed that around a nucleus alternating strata are superimposed, 

 which vary as the conditions for the excretion of the different ma- 

 terials have varied from time to time. The most common of these 

 stratified stones are composed of a nucleus of uric salts or of oxa- 

 late of lime covered by shells of phosphatic matter. 



The causes of urinary calculus are many, and in part still un- 

 known. The formation of uric-acid stones is ascribed to the long- 

 continued over-acidity of the urine, due either to the actual increase 

 in the quantity of the acid in the body as a result of imperfect oxy- 

 genation, to a sluggish mode of life, to a diet too rich in flesh, or to 

 lack of the supply of oxygen, or else to such an increase of the free 

 acids of the urine that the soluble uric salts which it contains are 

 decomposed, and the uric acid separated. This may proceed from 

 an acid fermentation within the organ, in which the coloring and 

 extractive matter of the urine turn into lactic acid, or else an acid- 

 ification in the primary passages favors such an excretion. Con- 

 ditions which produce a concentrated urine, as abstinence from 

 water, persistent diarrhoea, or badly-compensated heart-disease, may 

 also give rise to such excretion. 



Oxalate-of-lime stones, generally called mulberry calculi, have 

 likewise various modes of origin. Sometimes, when the urine is 

 alkaline, the acid f orms in the urine itself, probably through decom- 

 position of the uric acid. Sometimes the stone forms when the 

 diet has been exclusively vegetable, from excessive use of sorrel, 

 tomatoes, and the like. Again, these calculi may appear under con- 

 ditions of body not fully understood ; but, as we know, the charac- 

 teristic crystals of oxalate of lime are found in the urine of many 

 patients of sluggish habit, disordered digestion, or derangement of 

 the respiratory or nervous apparatus. 



Stones of phosphate of lime or ammonia, or of a mixture of the 

 two, are apt to form wherever a long-continued alkaline condition 

 of the urine produces alkaline precipitates in it. Such decomposi- 

 tion of the urine may proceed from chronic inflammation or other 

 diseases of the urinary tract, due to retention of urine. It may be 

 caused by the use of foul catheters, or by the presence of a foreign 

 body, such as a uric-acid or oxalate-of-lime calculus, which thus may 



