282 
NATURAL HISTORY. 
the due effect of this kind of decomposition, the vegetables should 
he heaped together, and their juices be abundant. In these circum¬ 
stances, the phenomena of decomposition are as follow: the colour 
of the vegetable is changed, the green leaves become yellow, the 
texture becomes lax, the parts less coherent, the colour of the vege - 
table itself changes to black or brown, the mass rises and perceptibly 
swells up, the heat becomes "more intense, and is perceived on ap¬ 
proaching the heap; and the fumes that arise have already a smell 
which sometimes is not disagreeable; at the same time bubbles arise 
and break at the surface of the liquid, when the vegetables are redu¬ 
ced to a magma , or mass of feculent matter. This gas is a mixture 
of nitrogen, hydrogen, and carbonic acid. At this epocha, likewise, 
an ammoniacal gas is emitted, which is formed in these circumstan¬ 
ces; and in proportion as these appearances diminish, the strong and 
offensive odour is succeeded by another"”which is fainter and milder, 
and the mass becomes dry. The internal part still exhibits the vege¬ 
table structure when the stem is solid, and the fibrous matter has 
been the predominating principle; and it then constitutes manure 
or soil. Hence it arises that the herbaceous plants of a loose tex¬ 
ture, and abounding in juices, are not capable of forming manure by 
their decomposition, but are reduced to a brown mass of little consis¬ 
tence, in which neither fibre nor texture is observed; and this is 
what for the most part forms vegetable mould.” 
This is decidedly one of the clearest descriptions that can possibly 
be given to the theory and phenomena of vegetable putrefaction. In 
the usual circumstances these are the following conditions : 
Impregnation, not maceration, with water, the contact of air, and 
the accumulation of the vegetable matter in a heap. The results are : 
a change of colour, a change of consistence, a rising or swelling up 
of the mass, a great degree of heat, the disengagement of foetid fumes, 
the envelopement of a combination of gases, the change of the vege¬ 
table substance into a magma or feculent mass, the drying of the re¬ 
mains into the form of manure, or vegetable mould. 
The required circumstances are:—Maceration in stagnant and 
unchanged water; the imperfect access of air by the interposition of 
the surrounding water; the loose contact of the stalks or leaves of the 
vegetables, owing to their partial diffusion in a fluid medium. In 
all cases of philosophical, and more especially in chemical investiga¬ 
tion, we are to consider causes and effects: the latter, by the im¬ 
mutable laws of nature,being the result of the former. If the causes 
(or circumstances) be precisely the same, the effects will exactly 
coincide ; but, if the effects are different, we must seek for the reason 
