ISO 



PRACTICAL PHYSIOLOGY. 



[XXIV 



© 





 







<:^ 



ii^ 



portion of blood-clot, or some albuminoid matter— in which crystals of oxalate 

 of lime or globular urates become entangled. Layer after layer is then de- 

 posited. In certain cases the nucleus may con- 

 y"--,^^ /—^ sist of a foreign body introduced from without. 



^^-V^ \ >Sr Calculi are sometimes classified as jirimanj and 



^^^ ^^ secondary ; the former are due to some general 



alteration in the composition of the urine, whilst 

 the latter are due to ammoniacal decom])Osition 

 of the urine, resulting in the precipitation of 

 Q phosphates on stones already formed. This of 

 course has an important bearing on the treat- 

 ment of calculous disorders. Calculi occur in 

 acid and alkaline urine. A higldy acid urine 

 favours the formation of t/ric ac?rf calculi, because 

 that substance is most insoluble in very acid 

 urine. A highly alkaline urine favours the for- 

 mation of calculi consisting of calcium phosphate or triple phosphate, as these 

 substances are insoluble in alkaline urine. 



Fig. 78.— Cystin. 



4. Method of Examining a Calculus 



(a.) Make a section in order to see if it consists of one or more 

 substances ; examine it with the naked eye, and a portion micro- 

 scopically. 



(b.) Scrape off a little, and heat it to redness on platinum foil 

 over a Bunsen-burner. 



FiO. 79. — a.a. Leucln balls ; b.b. Tyrosln sheaves ; e. Doable balls of 



ammonium mate. 



(A.) If it be entirely combustible^ or almost so, it may consist of 

 uric acid or urate of ammonium, xanthin, cystin, coagulated fibrin 

 or blood, or ureosteahth. 



