COLD. 1. In physics and physiology, a relative want of heat. Since there are no deter minate boundaries between cold and heat, it is a mere arbitrary distinction to call the degrees of the thermometer below the freezing-point de grees of cold. When the atmosphere, or any substance which comes in contact with the body, is at a lower temperature than the skin, it absorbs heat from the body, and is called cold. The physiological action of cold on the animal organism requires a brief notice. All animals (the warm-blooded animals to the greatest extent) have a certain power of main taining the heat of the body in defiance of ex ternal cold. This power is mainly due to a process analogous to combustion, in which car bon and hydrogen taken into the system in food are made to unite with oxygen derived from the air by respiration. If the combustible materials are not duly furnished, or if the supply of oxygen be deficient (as in various diseased conditions), there must be a depression of temperature. Now, if the temperature of a bird or mammal (except in the case of hibernat ing animals) be lowered about below its normal standard (which in birds ranges from 100° to 112°, and in mammals from 96° to 102°), the death of the animal is the result. The symptoms indicating that an animal or a man is suffering from a depression of the tem perature of the body are: (1) Retardation of the circulation of the blood, causing lividity of the skin, which is followed by pallor, in consequence of the blood being almost entirely driven from the surface through the contracting of the ves sels; (2) a peculiar torpor of the muscular and nervous systems at the same time, manifesting itself in an indisposition to make any effort or exertion, and in intense sleepiness. The respiratory movements become slower and the loss of heat goes on, therefore, with increasing rapidity, till the fatal limit is reached and death supervenes. In hibernating animals (the mar mot dormouse, bat, etc.) the power of generat ing heat within their own bodies is very slight, their temperature following that of the external air, so that it may be brought down nearly to the freezing-point. Great or prolonged atmos pheric cold is a most powerful depressing agent, and is a fruitful cause of disease and even of death. Whenever the temperature of the atmosphere is suddenly reduced, and par ticularly when it is reduced below the freezing point, a considerable addition takes place to the mortality of the region. The effects of cold are, in ordinary circumstances, most apparent among the aged and the very young, and among those suffering from chronic disease.
2. In medicine, cold, as well as heat, is fre quently employed for its therapeutic value. Cold is one of the most valuable means of ob taining lowered temperature. Cold sponging,
ice-packs, alcohol evaporation, are useful in most fevers, are indispensable in sunstroke and very refreshing in minor indispositions. Cold applied to an inflamed area diminishes the blood-tension by contracting the blood vessels, and thus tends to limit inflammation. Cold ap plied to the skin, as by a wet pack, or as a i shower, is a tonic, increasing metabolism, aug menting the appetite and giving mental and physical vigor. Cold applied as iced drinks, or cracked ice itself, is one of the best agents in nausea and gastric distress. Cold by means of ether or ethyl chloride spray is an excellent local anaesthetic for the treatment of local boils, felons, ulcers, etc., and is also used frequently in the extraction of teeth.
Catching cold is a term of wide popular use, and signifies an affection which is little treated of in medical literature, although an affection widespread and unpleasant. Catching cold is a process of disturbed equilibrium of the blood vessels. It is usually due to excessive evapora tion from the skin caused by drafts of air, to which is added contraction of the blood vessels of the periphery of the body, with consequent engorgement and congestion in some internal organ. Keeping quiet, taking hot foot-baths, or hot drinks, sweating, etc., are measures that tend to bring the blood to the contracted areas, and away from the congested areas, with consequent good results. If, however, the disturbance be comes marked, if the exposure has been exces sive, the congestion in an area becomes so seri ous that its local functions are diminished or aborted, and the congested blood vessels may be over-distended and paralysis result. Then an inflammatory reaction may ensue; the reduced vitality of the part encourages the multiplica tion of the ever-ready bacteria, and an acute diseased process may result. It may be a simple acute inflammation of the kidney; or if the pneumococcus is present in the lung, a pneu monia; or it may be a bronchitis. Taking cold is therefore a process that predisposes to more severe affections. In most cases the secondary reaction of taking cold manifests itself in the mucous membrane of the air passages, and running from the nose, some de gree of cough, general malaise, languor and muscular and joint pains are the results. Sec ondary infection, frequently through the super imposed influenza bacillus (if the condition be not primarily induced by that organism) results in the °grippe," following which bronchitis. and pneumonia are very frequent.
No cold in the head, no general cold should be neglected. Rest in bed, cathartics, hot drinks and medical advice are desirable.
For cold in physics, see' HEAT; THERMODY