DISEASES OF THE URINARY ORGANS. 135 



and mucus in addition to the mechanical injury caused by its pres- 

 ence. If such a body has been introduced through the solid tissues, 

 there is, in addition, the presence of the blood and lymph derived 

 from the wounded structures. 



CLASSIFICATION OF URINARY CALCULI. 



Urinary calculi are most conveniently divided according to the 

 locality in which they are found. Thus we find first renal calculi, 

 formed in the kidney (PI. XI, fig. 1), and which for cattle must be 

 again divided into calculi of the uriniferous tubes and calculi of the 

 pelvis. The second class are named ureteral calculi because they are 

 found in the duct leading from the kidney to the bladder (ui'eter). 

 The third class are the vesical calculi, from the bladder or vesicle in 

 which they are found. The fourth class are the urethral calculi, and 

 are foimd in the duct leading outward from the bladder through 

 the penis (urethra). The fifth and last class are the preputial cal- 

 culi, since they are found within the sheath of the penis (prepuce). 



Calculi may also be classed according to their chemical composition 

 and this has the advantage of suggesting the special cause of each as 

 found in the feed, water, soil, or general conditions of health. This 

 classification affords no guide to their location or symptoms, as cal- 

 culi of the same chemical composition may be formed at any part of 

 the urinary passages, as those formed in the kidney may pass on 

 through all the various passages outward, unless it is found at any 

 point of their progress that they have grown so large that the passage 

 will not admit them. The following are among the concretions found 

 in the various parts: 



(1) Coralline calculi. — These are of a dull- white color and irregu- 

 lar surface, like coral. They are made up of hard and resistant lay- 

 ers evenly deposited around a central nucleus. (PI. XI, fig. 3.) 

 Their specific gravity is 1,760, water being 1,000, and they contain 

 74 per cent of carbonate of lime with some carbonate of magnesia, 

 organic matter, and a trace of carbonate of iron. Yellowish-white, 

 smooth, round calculi of the same chemical composition are met with. 



(2) Pearly calculi. — These are more frequent than the first-named 

 variety. They are very hard and smooth on the surface, reflecting a 

 play of various colors after the fashion of a pearl. This peculiarity 

 appears to be caused by the thinness and semitransparency of the 

 supposed layers. They have a specific gravity of 2,109 to 2,351, and 

 nearly the same chemical composition as the coralline variety. Gold- 

 ing Bird found a specimen of this kind formed of carbonate of lime 

 Jind organic matter only. 



(3) Green calculi {metalloid calculi). — These are usually small and 

 numerous, as they are exceedingly common. They are of a very hard 



