122 



CHEMICAL PHYSIOLOGY. 



(c.) Cystin (very rare), hexa- 

 gonal crystals, soluble in 

 NH 4 ,HO (Fig. 31, a). 



(rf.) Leucin and Tyrosin 

 (very rare). (Fig. 32.) 



(e.) Cholesterin (very rare). 

 (Fig. 11.) 



(c.) Carbonate of Lime. 

 Small colourless balls, often 

 joined to each other; efferves- 

 cence on adding acids (micro- 

 scope). 



(d.) Crystalline Phosphate 

 of Lime. 



(e.) Leucin and Tyrosm 



(very rare). 



Fig. 31. a, Crystals of cystin; 6, oxalate of lime; 

 c, hour-glass forms of b. 



3. Urinary Calculi. 



They are composed of urinary constituents which form urinary 

 deposits, and may consist of one substance or of several, which 

 are usually deposited in layers, in which case the most central 

 part is spoken of as the " nucleus" The nucleus not unfrequently 

 consists of some colloid substance mucus, a 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 

 deposited. In certain cases the nucleus may consist of a foreign 

 body introduced from without. Calculi are sometimes classified 

 as jn'imary and secondary ; the former are due to some general 



