1 20 LESiSONS IN CHEinSTRT. 



175. So much, therefore, of the carbon of the mixed food 

 eaten by animals being thus separated in respiration, it is evi- 

 dent that the part which remains must become relatively richer 

 in nitrogen and the other ingredients ; and consequently, when 

 expelled from the body in the liquid and solid excrements, be 

 capable of exerting a more powerful effect as manure than 

 the same weight of the unaltered food applied to the soil. It 

 has been ascertained, by careful analysis of the food and 

 excrements of a horse fed on hay and oats, that, while in 

 the food, carbon and nitrogen existed in the proportion of 

 28 parts of the former to 1 part of the latter, in the dung 

 there were but 10^ parts of carbon to 1 part of nitrogen. 

 Thus, the investigations of the chemist beautifully confirm 

 the accuracy of the opinion long entertamed by practical 

 fanners. 



176. After the above remarks, you will readily understand 

 the explanation which chemistry affords of the difference in 

 the value of the manure produced by young animals and full- 

 gi'own cattle. In the droppings of 2i full-grown animal, you 

 have seen, the food eaten is discharged improved in its ferti- 

 lizing qualities; but, in the growing animal, much of the 

 gluten and inorganic matter of the food is employed in the 

 development of its bones and muscles ; hence the dung dis- 

 charged from the body is not so rich in nitrogen and saUne 

 matters. In fattening animals, the increase in bulk is pro- 

 duced not at the expense of the gluten and other nitrogenized 

 matters of the food, fat, like starch, containing no nitrogen 

 (78), and being formed from carbon, hydrogen, and oxygen 

 only ; nearly all the nitrogen therefore of the highly nutritious 

 food which the animals receive is discharged in their dung. 



177. Farm-yard Manure. — The refuse of the farm, the 

 straw used for litter, mixed with the liquid and solid excre- 

 ments of the cow-house, stable, and piggery, constitute what 

 is termed "farm-yard manure," which has long been regarded 

 as the most important source of the materials required for 

 the growth of the farmers' crops. It is generally supposed 

 that this manure must contain everything which plants 

 require for their nourishment, and to be all-sufficient to restore 

 fertility to any description of soil; but you will readily 

 understand, from what has been stated respectmg the varia- 

 ble composition of the excrements of animals, as well as of 

 the plants produced on the farm, that it must vary exceed- 



