386 PROFESSOR ALISON’S DEFENCE 
material facts on which this important discovery is founded:—‘ Nature has 
catenated together organic beings, and made them mutually dependent on each 
other for their existence, and all dependent on light. A privation of light would 
be immediately destructive to organic existence; vegetation would cease; the 
supply of oxygen gas would be quickly cut off from animals; the lower strata of 
the atmosphere would become composed of carbonic acid; and perception and 
volition would exist no longer.” * 
The following description of the circulation, in which all the matter destined 
by Nature to the maintenance of organised creation on the earth’s surface is con- 
tinually engaged, is merely an amplification of the expressions of Dumas; and 
although part of the statements contained in it are liable to objection, its general 
import is such as amply to fulfil the expectation of a great discovery which | 
had expressed. 
Vegetables, under the influence of light and of a certain temperature, are 
continually abstracting from the atmosphere, directly or indirectly, a part of its 
constituents, in the form of water, carbonic acid, a little nitric acid, and ammonia. 
The radicals of this inorganic matter (matiere brute) are gradually organised in vege- 
tables, which are a true reducing apparatus, while a part of its oxygen is set free ; 
and, after being formed into organic principles, those radicals are yielded directly 
or indirectly to animals. This matter is applied, without farther change, to the 
maintenance of the functions of animal life; particularly it furnishes the condi- 
tions, and becomes the instrument, of mental acts; after which, as if exhausted 
by the effort which it has made, it falls again under the influence of oxygen, 
in the animal body, which is a true apparatus of combustion ; and either before 
or after the death of the animal structure, returns as inorganic matter, under 
the name of manure, to the great reservoir from which it came. In this eternal 
circuit, life is the chief agent, and by these changes it makes itself known; but 
the matter that is thus employed undergoes only a change of place. I apprehend 
we must add, that the properties as well as the, position of this matter are conti- 
nually altered and resumed, and that it is the modification which the properties of 
this matter undergo, in the course of this circulation, which constitutes the pre- 
cise object of all physical inquiries, both in vegetable and animal physiology, so 
far as the organic functions of animals are concerned. 
The final cause of all these changes is already obvious. We know that it has 
pleased the Author of our being to connect with a world previously existing, and 
consisting of matter already long endowed with all its physical properties, an in- 
finite number and variety, and eternal succession, of sensitive creatures, and ulti- 
mately a race of beings “formed after his own image.” The acts of sensation 
and thought which characterise these, he has placed in immediate connection 
* Works, vol. i., p. 106. 
Pee oo ee ee 
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