142 NUTRITION OF FARM ANIMALS 



urine according as the intestines or kidneys form the normal 

 path of excretion, although they are contained to a small ex- 

 tent also in the perspiration. 



The intestines are the usual path of excretion for certain 

 mineral substances, notably iron, calcium and to some extent 

 magnesium. To these must be added in the case of the her- 

 bivora phosphoric acid, which, under ordinary conditions, is 

 excreted in the feces. The urine of herbivora, especially when 

 they consume roughage freely, or in more general terms when 

 the basic predominate over the acid ingredients of the ash, is 

 alkaline and contains but minute amounts of phosphoric acid. 

 On the other hand, during fasting or upon a ration having an 

 acid ash, the urine may have an acid reaction and then, like the 

 acid urine of carnivora or omnivora, may contain phosphoric 

 acid. The urine is the normal vehicle for the excretion of 

 sulphur, chlorin and the alkalies. 



200. Excretion of water. The motions of air in and out of 

 the lungs are the means of removing from the body more or 

 less incidentally large amounts of water by simple evapora- 

 tion. The presence of water vapor in the expired air is a fa- 

 miliar fact, shown by its condensation on a cold surface or in 

 cold air. The skin likewise acts, by means of its sweat-glands, 

 as a channel for the removal of water from the system, con- 

 siderable being continually evaporating from the skin in the 

 form of the " insensible perspiration." Under certain circum- 

 stances the excretion of water is so rapid as to give rise to the 

 formation of visible drops (sweating). 



The amounts of water excreted in these two ways are larger 

 than are sometimes realized. For example, a thousand pound 

 ox at ordinary temperature and on light feed may easily ex- 

 crete through the lungs and skin eight to ten pounds of water 

 in twenty-four hours, the amount depending to a considerable 

 extent upon the temperature and amount of movement of the 

 surrounding air. The feces also contain a large percentage of 

 water and in the case of herbivorous animals the amount thus 

 eliminated is very considerable. 



Finally, water is excreted in the urine, serving as a solvent 

 for the nitrogenous products of cell activity which are removed 

 through this channel. The amount of water thus excreted de- 

 pends in part upon the amount consumed, in part upon the 



