There is no principle in physiology better established than that which
considers vitality as a power engaged in continual conflict with the
physical, chemical, and mechanical laws, to which every species of
inanimate matter is invariably subject. Every phenomenon of the living
body might be advanced in illustration and support of this general
position. The animal machine is constantly surrounded and assailed by
agents, whose elective attractions for the principles of which it
consists, are so numerous and energetic, that its decomposition would
inevitably and speedily result, were not the adhesion of its molecules
maintained by the conservative influence of a superior power. The
compositions and decompositions which manifest themselves in the
elaborate operations of chylification, sanguification, and secretion,
are carried on by agencies totally distinct from those which govern the
combinations of inert matter, and must be investigated upon principles
essentially different. How then, it may be asked, can a medicinal
substance be brought to act _chemically_ upon the _living_ body?
Notwithstanding the general proposition, that the animal processes to
which we have alluded, are governed by laws peculiar to life, yet it
must be admitted that such processes are occasionally influenced,[177]
modified, and controlled by powers strictly chemical in their operation;
although in some cases it will be seen that such effects afford only
apparent exceptions to the general law: for several of the remedies
whose operations have been regarded as purely chemical, exert their
influence on parts which cannot be strictly considered under the control
of the living principle; of which _Antacids_, and certain _Antidotes_
and _Antiseptics_, to be hereafter explained, may be considered as
examples: in like manner will cataplasms of acetic acid hasten the
exfoliation of carious bone; a practice which has lately been employed
with much success in the Infirmary at Gloucester. Upon the same
principle alkaline applications may be made to dissolve coagulated
blood; suppose, for the sake of illustration, that the bladder should
become filled with coagulum through hemorrhage from the prostate gland,
and that the most serious consequences were to be apprehended from the
distention; in such an emergency, a dilute and tepid solution of potass,
if injected through the catheter, might prove eminently serviceable;
although such a practice would require the utmost skill for its safe
direction, since the removal of the plug, thus afforded by Nature to the
bleeding vessel, might be followed by an immediate return of active
hemorrhage. On the contrary, other agents destroy the vitality of the
organ before they can produce any change in the matter of which it is
composed, as the action of _Escharotics_ will clearly demonstrate.