together with the facility with which it may be 
made the subject of experiment, render our 
_ knowlege of its character and conditions nearly 
complete. 
_ When we have analysed these groups of 
ital phenomena and satisfied ourselves of the 
onditions under which they occur, we are 
rought to the conclusion that for each a parti- 
| cular organ or species of structure is appro- 
7 lated in the organized system, and that its 
ih on is dependent upon the excitation of its 
properties by agents external to it, just as in 
the inorganic world. This dependence of life 
upon external stimuli has been completely 
erlooked by the advocates of the vital prin- 
le ; and it is probably to Brown, with all his 
ults and absurdities, that we owe the first 
rominent enunciation of the fact. When these 
imuli are withdrawn, vital action ceases ; 
jough, under favourable conditions, vitality 
or the vital properties of the organism may be 
retained. (Sect. VI.) 
} Every class of organs in the living body may 
be said to require its particular stimulus for the 
play of its properties. Thus, regarding the 
; structure as a series of assimilating 
sans—capable of converting nutrient mate- 
into structures like their own, and of thus 
using them to exhibit vital properties—we 
ay say that the supply of these nutrient ma- 
rials in a fluid state is the stimulus to their 
on. Again, to the excretory organs the 
ired stimulus is the presence of certain 
aperabundant and therefore injurious elements 
1 the nutritious fluid. To the action of the 
uscular system the excitement of innervation, 
the application of a physical stimulus, is 
scessary. In all classes of living beings we 
ind these functional changes performed under 
onditions which are essentially the same; and 
ence we are enabled to arrive at the laws 
yhich regulate each. 
These are not the only conditions required, 
however; for others of a still more general 
ure are constantly, and therefore impercepti- 
ly, operating. All vital actions, for example, 
equite a certain amount of heat for their per- 
mance, and the amount varies in different 
This is ro more, however, than what 
meet with in the inorganic world ; for many 
‘chemical and physical operations can only take 
place within certain limits of temperature, and 
these sometimes very circumscribed. The pre- 
ence of light, again, is essential to many others, 
pecially in the vegetable kingdom; but this, 
Zain, finds its parallel in the inorganic world, 
ay chemical decompositions (which indeed 
a remarkable analogy with the changes 
thich this agent produces in the green parts of 
slants when exposed to an atmosphere contain- 
ing carbonic acid) being due to its influence. 
nd although, with regard to electricity asa 
Vital stimulus, our absolute knowledge is still 
less, what we do know leads to the belief that 
‘it is an agent of at least as much importance 
1 the vital economy as in the operations of in- 
organic nature. 
tien is nothing, then, in the nature or con- 
Ll 
te 
a 
ae 
z 
tions of vital actions considered individually, 
LIFE. 
147 
which need cause us to reason upon them in 
any other way than we do. upon the phenomena 
of the inorganic world; and it is obviously- 
unphilosophical to asswme an agency which is 
not required to account for them. It must be 
recollected, too, that the onus probandi rests 
with those who make the assumption, and not 
with those who maintain the analogy in the 
character of vital phenomena to those of the 
universe at large. ‘The assumption may be 
easily shown to be not only useless, but insuffi- 
cient to explain phenomena without calling to 
its aid the very principles. which have been 
shown to be themselves competent. Thus, the 
physiologist who traces the operation of the 
vital principle in the function of secretion, is 
compelled to allow that, as by one principle so 
great a variety of préducts are eliminated by 
the various glands from one material, the diffe- 
rence in the results must be due to some 
difference in the structure of the organs respec- 
tively concerned. And it may then be fairly 
inquired of him, “If the difference in the 
glandular structure and action is capable of 
giving rise to so great a variety in the products, 
with the cooperation of this one vital principle, 
how can it be proved that this difference in the 
glandular structure and action may not be capa- 
ble of giving rise to the same result by itself, and 
without the aid of any such adjunct at all?”* 
A similar question might be put with regard to 
any other class of actions, in which, under the 
same general conditions, the results are modified 
by the peculiar characters of the instruments or 
organs respectively employed ; and, as a nega- 
tive reply must be given equally to all, it may 
be safely affirmed that no reasoning can deduce 
the doctrine of a vital principle from the phe- 
nomena of life separately considered. 
But the advocates of the doctrine rely much 
upon the peculiar adaptation of the various 
changes taking place in each being to the pur- 
poses of its existence ; and assume that this 
adaptation can only result from the control 
of a subordinate presiding agent constantly 
exercised over each. Here, again, we find 
such a doctrine not only unsupported by, but 
manifestly inconsistent with, the analogies of 
nature. No reflecting mind has any doubt 
that this earth and its inhabitants form a system, 
of which every part is perfectly adapted to the 
rest, (so that we might almost call it an or- 
ganised one, if the idea of a particular struc- 
ture were not involved in the term,) and of 
which all the actions and changes, however in 
appearance contrary, have one common ten- 
dency—the ultimate happiness of the creatures 
of Infinite Benevolence. The same may be 
said of it in regard to its relations with the 
system of which it forms a part; and probably 
of that system with regard to the universe in 
which it is but a speck. So far as we can un- 
derstand the working of the laws by which that 
universe is governed, we see them all mutu- 
ally adapted to the same ends, whether we 
consider the welfare of the whole system, or of 
our own comparatively insignificant planet, with 
* Prichard on the Vital Principle, p. 100. 
L 2 
