24 VEGETABLE AND ANIMAL MANURES. 



2. The general composition of manures, natural and artificial. 



This is another branch of knowledge without which no use- 

 ful or comparative experiments can be made. 



Manures are generally classed under the three heads, of 

 vegetable, animal, and mineral. Those which are of vegetable 

 origin being formed of decaying vegetable matter, consist, like 

 the plant, of an organic and a mineral part, of which the former 

 is usually much the larger in quantity. But a new branch of 

 study is connected with the decay or decomposition of this 

 vegetable matter, and especially of its organic part, in the 

 farm-yard, in the compost-heap, or in the soil. This decay 

 gives rise to new chemical combinations which have much 

 influence on the efficacy of the decomposed matter as a manure. 

 The nature and products of this new series of chemical changes 

 ought not to be unfamiliar to the maker of useful and trustworthy 

 experiments. 



Those which are of animal origin resemble, of course, in 

 composition, the parts of the animal body from which they are 

 derived the blood, the flesh, the bone, &c. Or, if they con- 

 sist of the urine and droppings of animals, they have a certain 

 relation, especially the solid excretions, to the food on which 

 the animals have lived. Here, however, another new kind of 

 information is demanded. These animal substances, like those 

 of vegetable origin, putrify or decompose before they become 

 directly useful to plants. In the bodies of animals, also, changes 

 take place, by which the food consumed is decomposed, and new 

 compounds of much importance are, in consequence, introduced 

 into the urine and the droppings. All these changes are in some 

 degree connected with the richness and fertilising quality of ani- 

 mal manures, or with the special action of the variety which may 

 be used. To know on what the general efficacy or peculiar effect 

 of such manures depends, their changes, and the substances pro- 

 duced by them, should be understood. How different samples 

 of the same kind of manure differ in virtue ; how this virtue is 

 modified, lost, preserved, or augmented ; these questions are of 

 much consequence in ordinary farming, if the best or most pro- 

 fitable results are to be obtained by the practical man. But, in 



