342 MANURES. 



while another portion remains undigested, and passes the 

 bowels as solid dung corresponding to the soot of combus- 

 tion. This part of the dung, then, we see is merely so 

 much of the food as passes through the system without, 

 being materially changed. Its nature is easily understood. 

 It contains organic and mineral matters in nearly the con- 

 dition in which they existed in the hay. They have been 

 rendered finer and softer, but their chemical character 

 (their composition) is not materially altered. The dung 

 also contains small quantities of nitrogenous matter, which 

 has leaked out, as it were, from the stomach and intestines. 

 The digested food, how r ever, undergoes further changes 

 which affect its character, and it escapes from the body in 

 three ways i. e., through the lungs and skin, through the 

 bladder, and through the bowels. It will be recollected 

 from the first section of this book, p. 20, that the carbon in 

 the blood of animals unites with the oxygen of the air 

 drawn into the lungs, and is thrown off in the breath as 

 carbonic acid. The hydrogen and oxygen unite to form 

 a part of the water which constitutes the moisture of the 

 breath. 



" That portion of the atmospheric part of the hay which 

 has been taken up by the blood of the ox, and which does 

 not contain nitrogen, is emitted through the lungs. It con- 

 sists, as will be recollected, of carbon, hydrogen, and oxy- 

 gen, and these assume, in respiration, the form of carbonic 

 acid and water. 



