72 



small, glistening fat globules and granules. Some free fat i». 

 also usually found in the field. As fatty casts are secondary 

 products of epithelial and granular casts, the diagnosis of a 

 chronic process is justifiable. The hyaline matrix is character- 

 istic of the different varie- 

 ties of casts that have- 

 been mentioned up to this 

 point. 



Waxy casts differ in 

 chemical composition from 

 those previously m e n - 

 tioned. They are charac- 

 terized by wavy contours ; 

 a high refracting power; a 

 more or less yellowish 

 color and quite a high de- 

 gree of brittleness. They 

 FlG. 28. Waxy Casts. , , -^ - n T 



are slowly, ir at all, at- 

 tacked by acetic acid. Their presence signifies waxy degenera- 

 tion of the kidney. Hyaline casts may sometimes have a super- 

 ficial resemblance to waxy casts, but they never have the same 

 high refraction as the latter. 



In the urine of the horse, the sediment of crystals of lime car- 

 bonate may obscure the search for casts. In this case add a few 

 drops of acetic acid which will dissolve the crystals quickly, 

 and the casts, if present, will show more distinctly but undergo 

 solution more slowly than the crystals. 



Cast-like formations are composed of various elements having 

 a form somewhat similar to casts but lacking the matrix soluble 

 in acetic acid. Amorphous urates often simulate granular casts, 

 in form. Bacteria are often grouped in a manner similar to the 

 form of a cast, but a close inspection shows an irregular outline, 

 and usually a number of groupings not in cast form. Granular 

 detritus and hematoidin may also assume the form of casts ; like- 

 wise epithelial cells, blood corpuscles and fibrin in renal hempr- 

 rhages may also assume the form of casts. Acetic acid is said to 

 be a reliable reagent for differentiating between true and false 

 casts. This reagent dissolves the matrix of the true casts but does; 

 not act upon the cast-like formations. 



