REFRIGERANTS are remedial agents which directly diminish the force of the circulation, and reduce the heat of the body or a portion of it, without occasioning any diminution of the ordinary sensibility or nervous energy. This definition must not be considered as excluding cold from among the number of such because it is capable, when carried to extremes, of rendering the sensibility null, and utterly extinguishing the nervous power ; it is only its moderate and thera peutical employment which is here contemplated. Cold, however, has of late been recommended to be carried locally to an extreme degree, utterly destroying for a time and special purpose the sensibility, thus acting as an aneesthetio. It is likewise applied to the spine with much benefit in some cases of tetanus.
The manner in which refrigerants effect the ends which they accom. plish is far from being understood ; and a remarkable feature in their character is. that they display their peculiar effects chiefly when the action of the organs is above their natural standard, and more heat than natural is evolved. Till we have a perfect knowledge of the sources and mode of formation of animal heat, we are not likely to possess a correct theory of their mode of operating ; and at present, what ever plausibility the mere chemical hypothesis of Dr. Murray exhibits, we cannot consider the evolution of animal heat to be other than a vital process. This function is mainly carried on in the capillaries or extreme vessels, and is much influenced by the amount of supply of nervous energy to these vessels. Hence, when a limb is paralysed, it
is colder than the opposite sound member ; or when a single nerve is injured, the parts supplied by it have a lower temperature than the surrounding ones. Whatever, therefore, hinders the free communi cation of the nervous power to a part or to the whole system, will lessen its quantum of animal heat. By applying to the surface of the body any acid, the calibre of the capillaries is lessened, and hence the paleness which is observed, owing to less blood entering them. As the blood furnishes the pabulum from which the nerves evolve the heat, the less fuel the vessels contain, the less potent will be the heat resulting. The Introduction of any article of the class of refrigerants into the stomach appears to operate by sympathy on the whole vascular system, as may be seen in the case of dilute sulphuric acid checking hmmorrhage. The agents which are usually regarded as refrigerants are weak vegetable acids, or very greatly diluted mineral acids ; some saline, neutral, or super salts; and cool air, ice-cold water, and externally evaporating lotions. An indirect refrigerant is found in diminishing the quantity of animal food. [ANTIPIILOOISTIC TREAT. MENT; BATIHNO; LOTIONS.]