Cold is an agent peculiarly powerful in producing diseases, and removing them; indeed almost the fabled spear, which heals the wounds that it has inflicted. Though we have styled cold an agent, it is seemingly a privation of heat; and the application of cold to the human body, is only the application of such bodies which powerfully attract heat in consequence of their lower temperature: apparently, in some cases, from their possessing a greater affinity for caloric, or from carrying off heat in consequence of their evaporation.
In the human body, cold is a relative term. We style it cold when the thermometer is at 70°, if it has suddenly sunk from 84° to that point; but it is cold only at 32°, if the air has been long at 40°, with little wind. Temperate heat is generally placed at 62°; but the uniform heat of the earth in England is about 51°. From about these two last points-for, from many circumstances, there must be a considerable variety-cold diminishes the irritability of moving fibres: they contract more slowly; but, as cold condenses the skin, it presses more firmly on the subjacent vessels, and gives additional tone to the whole system. This effect of general pressure is evinced by the hilarity which we feel in a dense elastic atmosphere; and the same effect sometimes arises' even from the support of clothes: an advantage felt by the weak and irritable of the softer sex. In this state of the atmosphere, the perspiration is diminished; but the discharge of that gaseous, insensible halitus, which contributes so powerfully to our feelings of health, seems to be continued with unabated vigour, and to be occasionally increased. The discharges from the bronchial glands, from the lacrymal, and from those of the whole Schneiderian membrane, are augmented; and these, with the increased discharge of urine, seem chiefly to supply the deficiency of the perspiration: for in steady continued cold, the bowels are by no means relaxed, often in a contrary state.
The nervous system seems to suffer in nearly the same manner with the moving fibres. Its sensibility-is diminished; but the mental powers, we mean the intellectual, do not suffer. They seem to acquire vigour with the tone of the body; while tenderness, sensibility, and those feelings connected with an irritable system, arc, in proportion, less acute. The stomach, which partakes of the state of the nerves and moving fibres, experiences an increased tone. Its functions are less rapid, but performed more perfectly; and, for similar reasons, the bowels are frequently less active, and the nutritious particles, by delay, more completely separated. In short, if we were to fix the limits where the animal system was in its most perfect vigour, we should say it was in those regions where the heat seldom rises above 70°, or falls below 32°.
When, during a great part of the year, the heat is below the latter point, we find all the effects mentioned more striking, except the vigour of the intellectual faculties. When the irritability is further lessened, strength of mind becomes torpor; energy and vigour are sunk in sensibility, and roused only by violent causes to temporary exertions. When still further lessened, the distinguishing features of humanity are almost wholly lost. Even parental affection has little influence; and the great duties of religion are heard with indifference. The exertions necessary for the support of life, few as they are, occupy the mind and body. Love, which in warmer and more genial climates refines the heart, and awakens every finer feeling, here sinks into an animal passion, neither importunate nor refined; and the same want of irritability protracts the period of puberty, and lessens the proportional number of the offspring. A truly wise provision, where the means of support are so scanty.
The temporary effects of cold we have, in part, anticipated, under the article of bathing, q. v. All the changes just noticed come on rapidly; but the accumulated irritability, when no longer repressed, restores the glow. If, however, the cause continues, the debility is increased; the pulse flutters with an irregular, interrupted action; the senses become gradually weaker; a propensity to sleep so irresistible, that the victim is content to purchase it with his life, supervenes, and death creeps imperceptibly on this lethargy. The torpid animal, who passes his winter in this state of apparent death, recovers on the approach of spring. His irritability, suspended for a time, is accumulated; and he wakes from his death-like sleep with new vigour. When examined with a microscope, the vessels appear like dark lines; for the fluids are apparently coagulated. The action is first perceived in the vessels: this breaks the line into minute portions before these become un-distinguishable in a circulating fluid.
The partial action of cold has similar effects; but they are confined to the part only. The bulk of the organ is diminished; the vessels are less distinguishable; the skin becomes pale; and, if the cold is too long continued, its life is destroyed. Before, however, this last effect takes place, we avail ourselves of the change: the hernia is reduced; the puerperal discharge checked; inflammation diminished. 3 N 2
The diseases which cold produces are not numerous, if we speak only of continued cold. It checks, as we have said, the growth; it protracts the period of puberty; and renders the female less prolific. All these, however, are within the limits of health: and we may as well say, that the Italian female, full of fire and passion, is diseased from excess of fulness and irritability, as the Laplander from the defect of both. But, when the paucity of the menstrual discharge becomes a suppression; when the circulation can be no longer carried to the extremities, but chilblains and sphacelus affect the fingers and toes; when the whole system languishes; disease must be present. Yet, if we consider the variety of climates; the rigour of the arctic winters; the hardships of the Esquimaux, or of the sailor, in pursuit of the whale and seal; when we see, at the same time, the few diseases to which they are subject; we are almost tempted to assert, that continued cold is very rarely the cause of disease.