BaxgweLL.—Is Life a Distinct Force ? 415 
seo. The process by which a seed becomes a tree, producing other seeds 
like that from which it sprang, is clearly not the result of any one single 
force, unless we assume that that force was created and designed ad hoc ; 
neither heat, nor motion, nor light, nor electricity, nor chemical affinity, 
could alone cause the growth of a tree from a seed. Expose a seed to an 
amount of heat which will kill it without changing its chemical composition, 
and all the forces of uature will not enable that seed to germinate. What 
then do we kill? Even suppose that a living seed, exposed to the influence 
of heat and moisture, will swell by the mechanical process of endosmosis, 
suppose even we allow that the ovule will germinate, what possible com- 
bination of these or any other forces could make the radicle invariably push 
its way downwards into the soil, and the plumule as invariably thrust itself 
upwards towards the light? What combination of forces acting mechanic- 
ally and without intelligence could enable the cells of the young part to 
differentiate themselves and form the various tissues of which the plant is 
composed. Forces such as light and heat must always act under similar 
circumstances in the same way, unless guided and directed by a Supreme 
Intelligence. We are therefore driven, as it seems to me, to the conclusion 
that the force or energy which produces the phenomena that we collectively 
designate life, must be a force or energy of a special kind, created, if I may 
be allowed such an old-fashioned expression, ad hoc. In other words, that 
there is a vital force, which, acting on protoplasm, enables it to move to 
nourish itself, and to reproduce its like. 
I need say nothing about the other two qualities which enter into the 
definition of living matter— self-nutrition and reproduction—as it is nowhere 
disputed that these powers belong exclusively to living matter. 
Though, as I think, I have proved the vital force is a distinct and 
Special force, it has so much relation to the other forces of nature as to be 
convertible into them. ‘Thus in warm-blooded animals it is convertible into 
heat. That their animal heat is not the mere product of the chemical 
actions going on in their bodies is proved by the fact that precisely the same 
actions are going on in cold-blooded animals which do not maintain them- 
selves at a heat above that of the surrounding media. The muscular move- 
ments of a izard, for instance, in the tropics are extremely active, far more 
so than those of most of the warm-blooded vertebrates—yet the lizard is 
couch cooler tha» the surrounding atmosphere. We see another proof that 
the vital force of warm-blooded vertebrates is converted into heat, in the 
extreme difficuliy of maintaining the anima] heat of those who are weakly. 
Among human beings we who are practical physicians have constantly to 
recognize this fact. ‘The same external temperature which is pleasant and — 
even inspiriting io persons in vigorous health is depressing and injurious = 
and indeed often fatal, to those who are weak, 
