STABLE IMPURITIES. 47 



As the dung consists chiefly of cellulose and other insoluble 

 substances, its products of decomposition are unimportant ; 

 the chief ones being indole, skatole, lactic acid, and a trace ot 

 carbolic acid. Indole and skatole are complex ammoniacal 

 bodies, from which the dung derives its smell. The dung, 

 mixed with the alkaline fluid resulting from the decomposition 

 of the urine, forms an excellent breeding ground for bacteria, 

 the growth of which is unaffected by the small quantity of 

 carbolic acid which is present. The ferments secreted by 

 some of the bacteria have, like those of pus, the power of 

 dissolving albumen, and consequently they eat away those 

 portions of the horses' hoofs that come in contact with the 

 decomposing urine and dung. The fact of this liquid manure 

 being alkaline, also helps in the destruction of horn ; for the 

 matrix (chiefly mucin, which is nearly of the same com- 

 position as albumen) of the cells of the horn is soluble in 

 alkaline fluids. Prolonged maceration, even in water, also 

 causes disintegration of mucin, and consequent destruction of 

 horn. As ordinary water is not alkaline, and as it is not a 

 good medium for the cultivation of bacteria, its action on 

 horn would be far less destructive than that of a mixture of 

 decomposing urine and dung. Besides its comparatively slow 

 action on mucin, it softens, loosens, and consequently favours 

 the breaking down of horn cells. 



The ammonia in the air of the stable is an irritant to the 

 eyes and organs of breathing of horses. 



The ammonia has a bad effect on carriages, harness, and 

 saddlery, which are exposed to its influence, by dissolving resin 

 and fat with which it forms a soap. It also, like soda and 

 potash (p. 49) darkens brown leather, by combining with 

 the tannic acid which is in the leather. The varnish 

 on carriages is made by dissolving certain resins in spirit, 

 or in fixed or volatile oil, so that when the solvent evaporates, 

 it leaves a thin film of resin or shellac, for instance, behind. 



