476 PHYSIOLOGICAL CHEMISTRY 



In the chemical examination of urinary calculi the most valuable 

 data are obtained by subjecting each of the concentric layers of the 

 calculus to a separate analysis. Material for examination may be 

 conveniently obtained by sawing the calculus carefully through the 

 nucleus, then separating the various layers, or by scraping off from 

 each layer (without separating the layers) enough powder to conduct 

 the examination as outlined in the scheme (see page 477). 



Varieties of Calculus 



Uric Acid and Urate Calculi. Uric acid and urates constitute the 

 nuclei of a large proportion of urinary concretions. Such stones are 

 always colored, the tint varying from a pale yellow to a brownish-red. 

 The surface of such calculi is generally smooth but it may be rough 

 and uneven. 



Phosphatic Calculi. Ordinarily these concretions consist prin- 

 cipally of "triple phosphate " and other phosphates of the alkaline 

 earths, with very frequent admixtures of urates and oxalates. The 

 surface of such calculi is generally rough but may occasionally be rather 

 smooth. The calculi are somewhat variable in color, exhibiting gray, 

 white, or yellow tints under different conditions. When composed of 

 earthy phosphates the calculi are characterized by their friability. 



Calcium Oxalate Calculi. This is the hardest form of calculus 

 to deal with, and is rather difficult to crush. They ordinarily occur 

 in two general forms, i.e., the small, smooth concretion which is char- 

 acterized as the hemp-seed calculus, and the medium-sized or large stone 

 possessing an extremely uneven surface, which is generally classed as 

 a mulberry calculus. This roughened surface of the latter form of 

 calculus is due, in many instances, to protruding calcium oxalate 

 crystals of the octahedral type. 



Calcium Carbonate Calculi. Calcium carbonate concretions are 

 quite common in herbivorous animals, but of exceedingly rare occur- 

 rence in man. They are generally small, white, or grayish calculi, 

 spherical in form and possess a hard, smooth surface. 



Cystine Calculi. The cystine calculus is a rare variety of calculus. 

 Ordinarily they occur as small, smooth, oval, or cylindrical concretions 

 which are white or yellow in color and of a rather soft consistency. 



Xanthine Calculi. This form of calculus is somewhat more rare 

 than the cystine type. The color may vary from white to brownish- 

 yellow. Very often uric acid and urates are associated with xanthine 

 in this type of calculus. Upon rubbing a xanthine calculus it has the 

 property of assuming a wax-like appearance. 



