PHYSIOLOGY. 
coiild lift easily during life, shows how the 
laws of gravity are overcome. This vital 
power, in the explanation and illustration 
' of which all physiology is concerned, is so 
apparent in every living process, that it 
has been observed by the physiologists of 
every age, although designated by very va- 
rious appellations, and defined in very dif- 
ferent ways. Calidum innatum, arcliaeiis, 
spiritus vitalis, principium sentiens, &c. are 
among its numerous appellations. Let it 
be remembered, that neitlier these, nor the 
phrases of vital principle, &c. express any 
being existing by itselt^ and independently 
of the actions by which it is manifested ; 
they are only to be considered as denoting 
the assemblage of powers that animate liv- 
ing bodies, and distinguish them from inert 
matter. Some writers, realizing the off- 
spring of a mere abstraction, have talked 
of the living principle as something distinct 
from the body, to which they have ascribed 
powers of seeing and feeling, and even of 
acting with design. 
A more close inspection of any living 
body will speedily convince us, that this 
force, which holds together its component 
parts, in spite of the external powers, which 
tend to separate them, does not confine its 
influence to this passive result, but that 
its operation extends even beyond the limits 
of the living body itself. It seems, at least, 
that this power does not differ from that 
by which new particles are attracted, and 
interposed between the old constituent in- 
gredients of the body ; the latter effect 
•eeming to be exerted as constantly as the 
power by which the materials of the body 
are held together. For, besides the ab- 
sorption of alimentary matter from the in- 
testines, and its entrance into the circulat- 
ing fluid, carrying it to all parts, which pro- 
cesses experience no interruption, but are 
continued from one meal to another, there 
is another kind of absorption constantly go- 
ing on from the surface of the body, and a 
third which takes place by means of respi- 
ration. The two latter alone exist in such 
living bodies as have not the fimction of di- 
gestion ; riz. in plants. Now, since living 
bodies do not grow indefinitely, but have 
certain limits assigned by nature to their 
size ; they must lose on one side, at least, 
a large part of what they receive on the 
other ; and, in fact, attentive observation 
shows us, that perspiration, and several 
other processes, are constantly destroying 
parts of their substance. 
Hence the idea which we formed at first 
of the principal phenomenon of life, must 
be considerably modified. Instead of a 
constant union of the composing particles, 
we observe them in a state of continual cir- 
culation from without inwards, and from 
within outwards. Thus, a living body is a 
structure into which dead particles are suc- 
cessively brought, for the purpose of com- 
bining together in various ways, occupying 
places and exercising offices determined by 
the nature of the combinations into which 
they enter, and departing, after a certain 
period, to be brought under the action of 
those laws which regulate inanimate mat- 
ter. We must observe, however, that the 
proportion of particles, entering into or 
quitting the system, varies according to the 
age and health of the individual, and that the 
velocity of the general motion differs accord- 
ing to the different states of each living body. 
It appears, too, that life is arrested by 
causes similar to those which interrupt other 
known kinds of motion ; and that the indu- 
ration of fibres, and obstruction of vessels, 
would render death an inevitable conse- 
quence of life, as rest necessarily follows 
all movements which are not performed in 
vacuo, even if the hour of its approach were 
not hastened by a multitude of extraneous 
causes. 
This general and common motion of all 
parts constitutes the very essence of life, 
insomuch that parts separated from a living 
body immediately die, because they have 
no power of motion within themselves, and 
only jrarticipate in the general motion pro- 
duced by the assemblage. Thus, the peculiar 
mode of existence of any part of a living 
body arises from the whole ; while, in dead 
matter, each particle has it within itself. 
When this nature of life was once clearly 
recognised by the most constant of its ef- 
fects, physiologists naturally attempted to 
discover its origin, and the mode of its 
communication to bodies which it animates. 
They looked at them in their earliest state, 
approaching as nearly as possible to the in- 
stant of their formation ; but they could 
only discover them completely formed, and 
already possessing that circulatory motion, 
of which they were investigating the first 
cause. However delicate the parts of a 
foetus, or a vegetable, in the first moments 
that we can perceive them, they still pos- 
sess life, and have within themselves the 
germ of all the phenomena which this life 
will develope in the sequel. These obser- 
vations having been repeated in every class 
of living bodies, have led to the general 
