PRODUCTS, ADVENTITIOUS. 



75 



1. When the materials forming them are crys- 

 talline, minute crystals, the basis of the future 

 calculus, go on increasing in number, though 

 not individually in size, and by their accretion, 

 depending upon mutual attraction, form masses. 

 Animal matter may aid in cementing together 

 the constituent parts, but in this form of coales- 

 cence its occurrence to any amount is acci- 

 dental, and tends rather to diminish the firm- 

 ness of union. Pure uric acid calculi are formed 

 on this model. 2. When the substance form- 

 ing calculi is primitively amorphous, no attrac- 

 tion exists between the minute particles form- 

 ing the deposit ; hence a medium of union or 

 cement is necessary. This is furnished by 

 animal matters secreted with the urine, or 

 thrown out by the surfaces along which it 

 passes. The quantity and quality of these 

 matters being liable to vary, the general aspect 

 of the resulting calculus, and its properties of 

 density, &c., must be subject to similar variety. 

 Impure urate of ammonia calculi illustrate 

 this mode of formation. 3. In the 

 third species of aggregation, saline 

 particles in a semi-liquid state form 

 a sort of thick magma, as particu- 

 larly insisted on by M. Civiale* ; the 

 condensation of this magma produces 

 a uniform mass, or small spherical 

 bodies, or simply a pulverulent mat- 

 ter. This mode of formation is 

 chiefly observed in oxalate of lime 

 calculi, but occurs also in the uric 

 acid species mixed with various salts 

 (e.g. in a calculus in the University 

 College Collection composed of uric 

 acid, urate of ammonia, triple phos- 

 phate and phosphate of lime), and 

 in the phosphatic. 



The first deposition of matter from 

 the urine in these cases depends upon 

 some one or more of the causes we 

 have already enumerated in speaking 

 of the precipitation of the saline con- 

 stituents of secreted fluids generally. 

 If this matter be not expelled from the body, it 

 acts in various ways as a source of further de- 

 position and accumulation around itself; it is 

 for this reason called the nucleus, and the matter 

 accumulated around it the cortex, of the entire 

 mass. Every calculus may hence be theo- 

 retically resolved into a nucleus and cortex ; 

 but it is not the practice to give the central 

 part the former name, unless it be distinctly 

 different in composition, or, at least, in aspect, 

 from the matter immediately investing it ; there 

 are, therefore, practically speaking, non-nuclear 

 calculi, of which the pure uric acid and cystin 

 species furnish examples. 



The nucleus of a urinary calculus, although 

 commonly formed of sedimentary saline matter, 

 may likewise consist of various materials not 

 naturally existing in the urine, and these ma- 

 terials may be either formed in the body or 

 introduced from without. 



First: sedimentary nuclei may be composed 



* Trait^ de 1' Affection Calculeuse. 



of any one of the more important materials 

 (with perhaps a single exception) detected in 

 urinary calculi ; of these uric acid and oxalate 

 of lime are the most common, while the phos- 

 phate of lime and triple phosphate hold the 

 opposite position in the scale. A law esta- 

 blished by Dr. Prout, that " a decided deposi- 

 tion of the mixed phosphates is not followed 

 by other depositions," is, with few exceptions, 

 universal. Cystin has not (as far as we are 

 aware) been found playing the part of a nu- 

 cleus in any recorded case ; to this statement 

 a large calculus of cystin surrounded with a 

 very thin coating of phosphates (Univ. Coll. 

 Museum) cannot fairly be considered to sup- 

 ply an exception. 



A calculus commonly contains a single nu- 

 cleus only ; but instances are not wanting of 

 calculi containing two, three, and more nuclei. 

 Masses of the latter kind are probably simply 

 aggregations of smaller ones, as appears to have 

 been the case with that exhibited in^g. 74. 



Ftg. 74. 



Calculus urith " double nucleus" probably a double 

 calculus. (Univ. Col. Mus.) 



The mode of connection of the nucleus and 

 cortex varies. (1.) The union maybe inti- 

 mate and general by every point of the ap- 

 posed surfaces ; this is the most common case ; 

 (2.) the nucleus may adhere to the cortex by 

 asperities on its surface only ; empty spaces, 

 or spaces filled with grey gritty matter, being 

 interposed between them : (3.) the nucleus 

 may be free in the centre of the mass. Of the 

 latter rare state a striking specimen exists in 

 University College Museum ; the surface of 

 the nucleus is covered with dark-coloured 

 matter in powder (dried and altered blood), 

 some of which helps to fill the cavity existing 

 between the nucleus and cortex. 



The nucleus (when of the present species) is 

 generally the hardest part of a calculus. It 

 forms either in the kidney, or, much more 

 rarely, in the bladder. 



Secondly : animal matter, having such cha- 

 racters as render it impossible, according to 

 Berzelius, to determine whether it is composed 

 of mucus or of albumino-fibrinous substance, 



