204 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
Some nations have for long ages carried out the idea of pre- 
serving the fertility of the soil by this means a step further, and 
have made it the custom to apply to the land the manure from 
the human beings for whose support both crops and beasts are 
raised, and into which, therefore, the greater portion of the fer- 
tilising ingredients at last passes. 
The reason why the fertility of cultivated land is so easily 
exhausted was not known even by the best versed amongst our 
own forefathers, nor even to the nations who knew so well from 
a useful point of view how to dispose of human excreta. 
They could not answer the important question, "What are 
the substances which reduce the fertility of the soil by their 
loss? " or the equally interesting questions naturally following 
as to these substances being few or many ; whether all crops 
remove the same ingredients ; the proportions in which they are 
removed by different crops and systems of cropping ; the pro- 
portion in which they occur in the soil, and the proportions in 
which they are returned by the different forms of animal and 
vegetable refuse known as manures. 
The Value of Chemistry. 
Science, especially chemical science, has answered these 
questions for us, and so enabled us to make still better use of the 
manures already known and in common use, and it has done 
much more than this by suggesting that these fertilising and 
valuable ingredients of manure may be met with in other forms. 
By knowing exactly what to look for, it has found for us sources 
of fcrtihty, in some cases ready to our hands ; in other cases, 
existing in great deposits, which can be profitably brought even 
from far-off countries, and has discovered in the most unlikely, 
and apparently worthless, materials real mines of wealth when 
applied to the enrichment of the soil. 
It is not absolutely necessary now, as formerly, to test the 
value of a manure by trying it in the garden, since cliemical 
analysis will lind out for us whether it contains tlic proper fer- 
tilising ingredients, how mucli there is of them, and in wliat 
forms, and so will give an answer in a few lionrs, which will 
anticipate the result of months or years of experience. 
Hundreds and tliousands of tons of manure of all Ivinds arc 
houpfht and sold every year in tl)c markets on the result of 
