Substances which directly diminish the force of the circulation, and
reduce the heat of the body, without occasioning any diminution of
sensibility or nervous energy.
These remedies may be considered either as external and local, or as
internal and general. In the first case, there will not be much
difficulty in substantiating their claims to be considered _Chemical
Agents_, but in the latter case, the theory of their operation is
unsatisfactory and obscure; and even the facts which are adduced to
establish the existence of such a class of remedies, are of a very
problematical character.
TOPICAL REFRIGERANTS. In the case of external inflammation,
refrigeration may be produced by the application of cold substances,
such as water, ice, or certain saline solutions, or by the abstraction
of heat by means of evaporation, which is very effectually accomplished
by the use of lotions composed of spirit or ether. By these methods we
are capable of directly diminishing the activity of the vessels of the
part; thus, in burns and scalds, the pain is instantly relieved, and the
inflammation effectually reduced.
INTERNAL REFRIGERANTS. There are certain saline substances which, by
undergoing a rapid solution, and acquiring an increased capacity for
caloric, produce a diminution of temperature, and if this takes place in
the stomach, the sensation of cold which it will produce is equivalent
to a partial abstraction of stimulus; which, being extended by sympathy
to the heart, occasions a transient reduction in the force of the
circulation, and by this, or by a similar sympathetic affection, causes
a sensation of cold over the whole body; in this manner Dr. Murray
explains the refrigerant operation of nitre, which after all is of a
very doubtful nature. We shall perhaps not feel much difficulty in
accepting this theory, and in allowing that general refrigerant effects
may be temporarily produced, by occasioning an impression of cold upon
the stomach. The theory which is proposed to explain the refrigerant
operation of vegetable acids and certain other substances, and which we
have now to consider, is derived from those chemical views respecting
animal heat, in which the consumption of oxygen in the act of
respiration is considered the principal source. Dr. Murray,[178] who has
given a luminous exposition of this theory, says “it is established by
numerous experiments and observations, that the quantity of oxygen
consumed in the lungs is materially influenced by the nature of the
ingesta received into the stomach. When the food and drink are composed
of substances which contain a small proportion of oxygen, it is known
that the consumption of oxygen in the lungs is increased, and this even
in a short time after the aliment has been received; thus Mr. Spalding,
the celebrated diver, observed, that whenever he used a diet of animal
food, or drank spirituous liquors, he consumed in a much shorter time
the oxygen of the atmospheric air in his diving-bell; and therefore he
had learned from experience to confine himself to a vegetable diet, and
to water for drink, when following his profession.”[179] During
digestion too, it was established by the experiments of Lavoisier and
Seguin, that a larger proportion of oxygen than usual is consumed.
But it is known, that the animal temperature is derived from the
consumption of oxygen gas by respiration; and, that an increase in that
consumption will occasion a greater evolution of caloric in the system,
and consequently an increase of temperature in the body, while a
diminution in the consumption of oxygen will have an opposite effect.
If, then, when the temperature of the body is morbidly increased, we
introduce into the stomach substances containing a large proportion of
oxygen, especially in a loose state of combination, we may succeed in
reducing the general temperature. This we accomplish in part by a
vegetable diet, but still more effectually by the free use of the
_Acids_. The vegetable acids in particular, which are found by
experience to be the best refrigerants, are readily acted upon by the
digestive powers, and assimilated with the food; and as the large
quantity of oxygen which they contain is already in a concrete state,
little sensible heat can be produced by the combination of that element
with the other principles of the food. The nutritious matter which is
received into the blood, containing thus a larger proportion of oxygen
than usual, will be disposed to abstract less of it from the air in the
lungs, and consequently less caloric will be evolved; the temperature of
the body will be reduced; and this, again operating as a reduction of
stimulus, will lessen the number and force of the contractions of the
heart.
Such is the philosophical web which chemical ingenuity has wove for
us,—the device is beautiful, but the fabric will be found too frail to
endure the touch. The experiments of Dr. Crawford, in proof of the
chemical origin of animal heat, are highly ingenious and plausible, but
it is now generally admitted that the temperature of animals depends
upon the living principle[180] which animates them, and that although
the absorption of oxygen, in the act of respiration, may directly
contribute something to its production, yet that its chief action is
that of serving as a stimulus to the living power in generating it; for,
as Sir Gilbert Blane[181] remarks, oxygen plays an interesting and
active part as an exciting power throughout all nature, both animate and
inanimate. If the heat of the body depended on respiration alone, any
one might, by a voluntary effort of quick, deep, and prolonged
respiration, increase the temperature of his body at will; the effect
also of the emotions of the mind, in generating both heat and cold, adds
Sir Gilbert, is proof sufficient of temperature depending on a vital,
and not on a chemical cause.