132 



DISEASES OF CATTLE. 



into the urine. Now, carbonate of lime is soluble in water containing 

 free or uncombined carbon dioxid, but is precipitated whenever the 

 latter is withdrawn. It is only necessary, therefore, to have in the 

 urine sufficient lime or other available base to unite with all the free 

 carbon dioxid in order to bring about the precipitation of the dis- 

 solved carbonate of lime in the solid crystallized form. Hence it is 

 that, of all sediments in the urine of herbivora, this is the most fre- 

 quent and usually the most abundant. 



A less common constituent of urinary calculi is the insoluble oxalate 

 of lime. In this case the lime is derived as before from the food or 

 water, or both, while the oxalic acid is a product of the oxidation of 

 organic acids of the food, less oxygen having been used than in the 

 formation of carbon dioxid. The final product of the complete oxida- 

 tion of these acids is carbon dioxid, but when less oxygen is furnished 

 owing to some disease of the lungs or a disease of the nerve centers, 

 which lessens the activity of the breathing, then oxalic acid may be 

 produced. Then if this oxalic acid comes in contact with lime, it is 

 instantly precipitated as crystals of oxalate of lime. 



Another inorganic substance at times found in urinary calculi is 

 silica (Si0 2 ). This contributes largely to giving stiffness to the stems 

 of growing plants, and in most of our cereals and grasses makes up a 

 large proportion of the ashes of the burnt plant. It is found in the 

 soluble form in combination as silicate of potash, but at times is dis- 

 placed by oxalic or other acid and then appears as gritty, sandy par- 

 ticles in the stem. This gritty, insoluble silica is especially noticeable 

 among the horsetails (Equisetacece,) , bamboos, and sedges. The per- 

 centage of silica in the ash of several common fodder plants is given 

 below : 



Silica in ash of various fodder plants. 



Ash of- 



Wheat straw. . 

 Oats and husk 



Oat straw 



Barley straw. . 

 Eye straw — 



Silica. 



Percent. 

 67.6 

 88.6 

 35.4 

 73.1 

 64.4 



Ash of— 



Bye-grass hay 

 Wheat chafe . . 



Oat chaff 



Barley awn 



Silica. 



Percent 

 64.57 



81.2 

 59.9 

 70.7 



It is only soluble silica that is taken up into the system, and it is in 

 this form (usually as silicate of potash or soda) that it enters the urine, 

 but all that is wanted to precipitate it in crystalline form as a gritty 

 sand is the presence of oxalic or other acid having a stronger affinity 

 for its base (potash or soda). 



Other conditions, however, enter largely into the causation of stone, 

 or gravel. A high density of urine resulting from a highly saturated 

 condition is often present for a length of time without any precipita- 

 tion of solid materials. Urea and carbonates may be present in 



