MANURES. 343 



" The atmospheric matter of the digested hay, in the 

 blood, which does contain nitrogen, goes to the bladder, 

 where it assumes the form of urea a constituent of urine 

 or liquid manure. 



" We have now disposed of the imperfectly digested food 

 (the dung), and of the atmospheric matter which was taken 

 up by the blood. All that remains to be examined is the 

 earthy matter in the blood, which would have become ashes 

 if the hay had been burned. The readily soluble part of 

 this earthy matter passes into the bladder, and forms the 

 earthy parts of urine. The more insoluble part passes the 

 bowels, in connection with the dung. 



" If any of the food taken up by the blood is not returned 

 as above stated, it goes to form fat, muscle, hair, bones, or 

 some other part of the animal ; and as he is not growing 

 (not increasing in weight), an equivalent amount of the 

 body of the animal goes to the manure to take the place of 

 the part retained.* 



" We now have our subject in a form to be readily under- 

 stood. We learn that when food is given to animals it is 

 not put out of existence, but is merely changed in form 

 and that in the impurities of the breath we have a Iarg6 

 portion of those parts of the food which plants obtain from 

 air and from water ; while the solid and liquid excrements 



* This account of digestion is not, perhaps, strictly accurate in a physiological 

 point of view, but it is sufficiently so to give an elementary understanding of 

 the character of excrement as manure. 



