Digestion. 153 



the downy hair found on the kernel of oats, vegetable tubes 

 and spirals, starch and fat granules, gums, resins, chloro- 

 phyl, etc. ; unabsorbed proteid, carbo-hydrate and fatty 

 material ; products of digestive fermentation, such as 

 lactic, malic, butyric, succinic, acetic, and formic acids ; 

 leucin, tyrosin, indol, skatol, and phenol ; biliary matters 

 and altered bile pigment, which latter gives the colour to 

 the dejecta, and is known as stercobilin ; and, lastly, 

 mineral matter in varying proportions. The faeces always 

 float in water. 



Amongst the inorganic matter silica exists in largest 

 amounts, then potassium and phosphoric acid, sodium, lime, 

 magnesium, and sulphuric acid, forming a smaller but still 

 important proportion. 



The horse excretes but little phosphoric acid by the 

 kidneys, but considerable quantities pass with the feces in 

 the form of ammonio-magnesium phosphate. This salt is 

 derived principally from the oats and bran of the food, and 

 through collecting in the colon and becoming mixed with 

 organic substances, frequently forms itself into calculi. 

 Other intestinal calculi are formed from lime deposits in 

 the bowel, and collections of the fine hairs from the kernels 

 of oats form the so-called oat-hair calculus. 



The following table by Roger gives the mineral com- 

 position of the faxes in every 100 parts of the ash :* 



