ON MANURE. 



59 



ceases. The plants now find those sub- 

 stances which formerly prevented their 

 growth removed, and in their place meet 

 with humus, that is, vegetable matter in the 

 act of decay. 



We can scarcely suppose a better means 

 of producing humus than by the growth of 

 plants, the leaves of which are food for ani- 

 mals ) for they prepare the soil for plants of 

 every other kind, but particularly for those 

 to which, as to rape and flax, the, presence 

 of humus is the most essential condition of 

 growth. 



The reasons why this interchange of crops- 

 is so advantageous the principles which 

 regulate this part of agriculture, are, there- 

 fore, the artificial production of humus, and 

 the cultivation of different kinds of plants 

 upon the same field, in such an order of 

 succession, that each shall extract only cer- 

 tain components of the soil, whilst it leaves 

 behind or restores those which a second or 

 third species of plant may require for its 

 growth and perfect developement. 



Now, although the quantity of humus in 

 a soil may be increased to a certain degree 

 by an artificial cultivation, still, in spite of 

 this, there cannot be the smallest doubt that 

 a soil must gradually lose those of its con- 

 stituents which are removed in the seeds, 

 roots, and leaves of the plants raised upon 

 it. The fertility of a soil cannot remain un- 

 impaired, unless we replace in it all those 

 substances of which it has been thus de- 

 prived. 



Now this is effected by manure. 



CHAPTER IX. 



OF MANURE. 



WHEN it is considered that every consti- 

 tuent of the body of man and animals is de- 

 rived from plants, and that not a single 

 element is generated by the vital principle, 

 it is evident that all the inorganic constitu- 

 ents of the animal organism must be re- 

 garded, in some respect or other, as manure. 

 During their life, the inorganic components 

 of plants which are not required by the ani- 

 mal system, are disengaged from the orga- 

 nism, in the form of excrements. After 

 their death, their nitrogen and carbon pass 

 into the atmosphere as ammonia and car- 

 bonic acid, the products of their putrefac- 

 tion, and at last nothing remains except the 

 phosphate of lime and other salts in their 

 bones. Now this earthy residue, of the pu- 

 trefaction of animals must be considered, in 

 a rational system of agriculture, as a power- 

 ful manure for plants, because that which 

 has been abstracted from a soil for a series 

 of years must be restored to it, if the land 

 is to be kept in a permanent condition of 

 fertility. 



ANIMAL MANURES. 



We may now inquire whether the excre- 



ments of animals, which are emplo\cil as 

 manure, are all of a like nature and power, 

 and whether they, in every case, administer 

 to the necessities of a plant by an identica 

 mode of action. These points may easily 

 be determined by ascertaining the composi- 

 tion of the animal excrements, because we 

 shall thus learn what substances a soil really 

 receives by their means. According to the 

 common view, the action of solid animal 

 excrements depends on the decaying orga- 

 nic matters which replace the humus, and 

 on the presence of certain compounds of 

 nitrogen, which are supposed to be assimi- 

 lated by plants, and employed in the pro- 

 duction of gluten and other azotised sub- 

 stances. But this view requires further 

 confirmation with respect to the solid excre- 

 ments of animals, for they contain so small 

 a proportion of nitrogen, that they cannot 

 possibly by means of it exercise any in- 

 fluence upon vegetation. 



We may form a tolerably correct idea of 

 the chemical nature of the animal excre- 

 ment without further examination, by com- 

 paring the excrements of a dog with its 

 food. When a dog is fed with flesh and 

 bones, both of which consist in great part 

 of organic substances containing nitrogen, a 

 moist white excrement is produced, which 

 crumbles gradually to a dry powder in the 

 air. This excrement consists of the phos- 

 phate of lime of the. bones, and contains 

 scarcely J^-Q part of its weight of foreign 

 organic substances. The whole process ot 

 nutrition in an animal consists in the pro- 

 gressive extraction of all the nitrogen from 

 the food, so that the quantity of this element 

 found in the excrements must always be 

 less than that contained in the nutriment. 

 The analysis of the excrements of a horse 

 by Macaire and Marcet proves this fact com- 

 pletely. The portion of excrements sub- 

 jected to analysis was collected whilst fresh, 

 and dried in vacuo over sulphuric acid ; 100 

 parts of it (corresponding to from 350 to 

 400 parts of the dung before being dried) 

 contained 0.8 of nitrogen. Now every one 

 who has had experience in this kind of ana- 

 lysis is aware that a quantity under one per 

 cent, cannot be determined with accuracy. 

 We should, therefore, be estimating its pro- 

 portion at a maximum, were we to consider 

 it as equal to one-half per cent. It is cer- 

 tain, however, that these excrements are not 

 entirely free frorn nitrogen, for they emit 

 ammonia when digested with caustic potash. 



The excrements of a cow, on combustion 

 with oxide of copper, yielded a gas which 

 contained one vol. of nitrogen gas, and 26.30 

 vol. of carbonic acid. 



100 parts of fresh excrements contained 



Nitrogen 

 Carbon . 

 Hydrogen 

 Oxygen . 

 Ashes . 

 Water 



. 0.506 

 . 6.204 

 . 0824 



. 4.818 

 .. 1.748 

 . 85.900 



100.000 



