78 



insoluble in cold and hot urine and in weak 

 acids, soluble with effervescence (from equal 

 volumes of carbonic acid and nitrogen) in con- 

 centrated nitric acid, the mixture acquiring a 

 purple red hue (from murexide) at the close of 

 evaporation, and very sparingly soluble in 

 concentrated muriatic acid. (See fig. 78, a.) 

 Fig. 78. 



PRODUCTS, ADVENTITIOUS. 



Crystals of uric acid. 



Sometimes (and less rarely than has been sup- 

 posed) the rhomboidal prisms are thick, solid- 

 looking, and cuboid in appearance. We have 

 lately seen a/W/He^non-irridescent) of bloody 

 urine after scarlatina formed of crystals of 

 this kind (fig. 78, 6). Sometimes, again, frag- 

 ments of, or entire, crystals unite so as to 

 form lanceolate or stellate figures ; this form 

 may be produced '(as shown by Rayer, fig. 

 78, c) by artificial precipitation. 



2. The urate of ammonia calculus (of which 

 the existence was denied by Mr.Brande, on the 

 plea that the ammonia evolved from certain 

 calculi is in reality derived from associated 

 triple phosphate, or from urea and the ammo- 

 niacal salts of the urine,) is said by Fourcroy 

 and Prout to be rare, and more frequent in 

 children than in adults, a statement which has 

 been copied by various writers. The tables 

 collected by Dr. Prout show that of 709 simple 

 calculi 59 were composed of urate of ammonia 

 nearly pure, 159 mainly of this salt mixed with 

 variable proportions of the urate and oxalate of 

 lime and phosphates. The shape of this cal- 

 culus is more irregular than that of uric acid 

 masses, but still inclined to the ovoid ; it does 

 not reach any large size, and has a smooth or 

 granular surface. Internally it is laminated; 

 of clay colour ; its fracture earthy, and its den- 

 sity considerably less than that of lithic acid. Of 

 163 alternating* calculi grouped in Dr. Prout's 

 tables we find that 239 had a nucleus of pure 

 urate of ammonia. In the majority of cases, 

 then, this salt or uric acid forms the ground- 

 work of calculous accumulation ; for they con- 

 stitute either the entire mass, or the nucleus, 

 of 938 among 1473 calculi of ascertained com- 

 position in the following proportions, exclusive 

 of many others in which they were mixed 

 irregularly with other saline matters. 



Calculus. Nucleus. 



Uric acid, .. 230 251 



Urate of ammonia"! 



pure and impure J 



218 



448 



239 



490 



Urate of ammonia is the chief constituent of 

 the pulverulent sediments of urine voided by 

 healthy persons : it is insoluble in cold, soluble 

 in hot, urine. It is commonly distinguished 

 microscopically as a pulverulent closely packed 

 matter (fig. 79, a) ; in other instances it wears 

 the form of globules of black colour * (fig. 79, 

 b} ; when alkaline reaction is established (or 

 sometimes, as we have seen, while the urine is 

 still acid) these globules become stellate from 

 the formation of minute silky needles apparently 

 springing from their circumference (fig. 79, c). 



Fig. 79. 



938, or 1 in I '6 



a, b, c, Deposits of lithate of ammonia. (After\Rayer.} 



Treated by dilute nitric acid, the pulverulent 

 matter is converted into rhomboidal crystals 

 of uric acid, fig. 78. Collected on a filter and 

 washed with rectified alcohol, the residue of 

 the amorphous matter, treated with potassa, 

 disengages ammonia, to be detected by the 

 smell, test paper, and hydrochloric acid. The 

 forms b and c cannot be confounded with any 

 other substance ; the pulverulent form might 

 be mistaken for phosphate of lime, and the 

 modes of distinguishing the two precipitates are 

 explained with the description of the latter. 

 The forms b and c (first described by Qaevenne) 

 we have repeatedly observed in the sediment 

 of urine containing lithates in abundance. 

 Though mainly composed of urate of ammonia, 

 the acid is apparently in union also with potass, 

 soda, lime, and magnesia. Quevenne considers 

 that they may in some sort be regarded as pro- 

 ducts of putrefaction, as they do not appear 

 until the urine has stood for about three days ; 

 but this is decidedly erroneous, as we have re- 

 peatedly seen the simple globular, and some- 

 times the stellate globular, forms in urine which 

 had not stood twenty-four hours. 



3. The oxalate of lime calculus is generally 

 more or less accurately spherical in shape ; 

 though commonly of rather small or moderate 

 size, it may acquire very considerable bulk : a 

 model of a mulberry calculus, now before us, 

 (Univ. Coll. Museum) measures 7f inches in 

 circumference, and some of the prominences on 

 the surface reach five lines in height. Of dark 

 brown, purplish, blackish, or olive colour, this 



* This form, which we are in the habit of fami- 

 liarly calling the " globular lithate," is not exceed- 

 ingly uncommon. In the numerous instances in 

 which we have met with it, we have, however, 

 failed in ascertaining the particular condition regu- 

 lating its occurrence. 



