REVIEW—ORGANIC CHEMISTRY. 753 
The statement, that on the presence of humus depends the ferti¬ 
lity of soil, is combatted by him. 
“ The opinion that the substance called humus is extracted from the soil by 
the roots of plants, and that the carbon entering into its composition serves, 
in some form or other, to nourish their tissues, is so general and so firmly 
established, that, hitherto, any new argument in its favour has been considered 
unnecessary; the ob\'ious difference in the growth of plants, according to the 
known abundance or scarcity oihumus in the soil, seemed to afford incontestible 
proof of its correctness. Yet this position, when submitted to strict examina¬ 
tion, is found to be untenable, and it becomes evident, from most conclusive 
proofs, that humus, in the form in which it exists in the soil, does not yield the 
smallest nourishment to plants.” 
This view he substantiates by a reference to the facts, that the hu- 
mic acid of chemists, the of vegetable physiologists, when first 
precipitated, requires 2500 times its weight of water to cause it to 
undergo solution, and only when newly-precipitated is it soluble at 
all, becoming completely insoluble when dried in the air, or when 
exposed in a moist state to a freezing temperature; so that both ■ 
the cold of winter and the heat of summer are destructive of the 
solubility of humic acid, and, at the same time, of its capability of 
being assimilated by plants. 
This circumstance has not been unnoticed by vegetable physio¬ 
logists, and they have supposed that the lime, or the different alka¬ 
lies found in the ashes of vegetables, render soluble the humic acid 
and fit it for the process of assimilation. He afterwards goes on 
to shew, by a reference to the constitution of vegetables, that, al¬ 
though alkalies and alkaline earths do exist in sufficient quantities 
in different soils to form soluble compounds with humic acid, and 
the most soluble of these is the humate of lime, yet this will not 
account for the amount of carbon met with in the plant, not even if 
the most favourable circumstances are taken into consideration by 
which humic acid is received, namely, the agency of rain-water. 
As to manure —“ It is not denied that manure exercises an influence upon 
the development of plants ; but it may be affirmed with positive certainty, that 
it neither serves for the production of carbon, nor has any influence upon it, 
because we find that the quantity of carbon produced by manured lands is 
not greater than that yielded by lands which are not manured. The carbon, 
then, must be derived from other sources, and it can only be extracted from 
the atmosphere.” liy calculation is then demonstrated the amount of carbonic 
a(;id given out during the respiration of man and animals, leaving unnoticed 
the many other sources whence this gaseous compound is also derived; and 
from this is proved the hecessity of those beautiful reciprocating laws that 
obtain in the economy of nature, which arc proofs of order and design in Him 
by whom all things were made and continue to exist. “ The life of plants is 
closely connected with that of animals, in a most simple manner, and for a 
wise and sublime purpose.” 
The essential (onstituont? of plants having been demonstrated to 
bo the elements of water with carbon, the inquiry arises, 
