What happens, in as far as these different con stitutions are concerned, when the change of season is the opposite of that we have just dis cussed ? when the progress is from the colder to the hotter period of the year ? The constitu Lions that have just been particularly mentioned, it is obvious, will find themselves benefited by the change ; they are continually supplied with larger proportions of heat of which they were especially in want. But robust constitutions, in which the calorific faculty is largely deve loped, will they not be in an opposite position, unless the energy of the faculty in question diminishes in proportion as the external tem perature increases ? This in fact is what of necessity happens to those in whom the power of accommodation is defective. For when the calorific faculty continues in full force, when the temperature of the surrounding atmosphere is high, there is an excess of heat proceeding from within as well as from without ; and if the body does not suffer in the first instance, which it is apt to do, it before long feels the deteriorating influence of this ndditional excitement, which then superinduces a series of morbid phenomena of various degrees of intensity according to circumstances. All this is observed to occur in the most distinct manner among the natives of cold climates who come to reside in very hot countries. The most robust are even observed to be the most apt to sufkr from the change, and the effect is so decided, that few escape some derangement of health, occasioned solely by the influence of the high temperature. When the affection appears in the acute form, after recovery, the new comer is said to he seasoned. The constitution appears to have suffered a favour able change, which consists essentially in a decrease of the faculty to produce heat. In fact it is often only by a process of this kind that the calorific power can be brought into harmony with the new circumstances in which it is placed.
Something of the same kind even takes place in the constitutions of the inhabitants of the countries which have two very different temperatures during the two halves of the year. Here, however, the change of constitution ge nerally passes insensibly or nearly so, the transition being both less in itself, and the natives being accustomed to the difference. Let us just remark that we have here another instance of the vis medicatrix nature, the ten dency of which at all events is salutary, but of which the violence of effect by exceeding the proper limit frequently becomes fatal. We even perceive here that nature has two pro cesses at her command, by which she adapts us to changes of external circumstances ; the one is gradual and insensible, the other is sudden and violent.
From repeated observation, and from experi ments upon the effects of exposure to high tem it is easy to infer the general charac ter of the disease in its simplest form, which the natives of cold climates will be likely to con tract in hot countries. As a high temperature of the air accelerates the breathing and excites the circulation, it may arouse these functions to such a pitch, that the condition becomes truly pathological, and the disease which results is continued fever with excessive heat of surface in those countries where the external conditions are subject to little variety.
There are other phenomena accompanying changes of climate that are referable rather to the state of health than to any morbid condition that bears upon the sensations. It is a general re mark that natives of the warmer regions of the earth, of a good natural constitution, when they visit countries within the temperate zone, suffer little from the effects of cold the first winter ; on the contrary, they seem to live very much at their case, except in extreme cases. Let us see
if we can explain this fact with the assistance of the principles established above. If the natives of warmer climates come during the summer to temperate countries, they experience a change of no great amount indeed, and which, in the generality of cases, is not obvious. The heat grows less and less intense, declining gradually; freshness or coolness succeeds ; then comes moderate, and at last severe cold. NVell constituted individuals, therefore, and they may be assumed as the majority, will experi ence the general influence of a gradual cooling process ; that is to say, their faculty of produ cing heat will increase, whence will result a feeling of warmth and of comfort. But this faculty has its limits of increase, which in fact lie within narrower bounds than in the ease of well-constituted natives of temperate climates. They are consequently apt at length to fall short of the mark, and so to remain, in regard to calorifieation, under the standard necessary to the economy. NVIienever the progression of which we have spoken ceases, which hap pens in the course of the second winter, these individuals begin to experience the uneasiness which results from its deficiency. It is easy to confirm and render manifest the justice of the above deduction by means of a simple yet curious experiment. If a person having wares hands will keep one plunged for some time in water near the freezing point, it becomes chilled of course, but reaction will be observed soon to take place, and the hand will become red. If it be now taken out of the water and wiped dry, the individual being all the while in a cool at mosphere, at or 12° c., the hand will by-and by begin to glow, and the feeling in it will be that of a temperature considerably above the heat of the other hand ;—judging by the feeling alone the hand seems hotter than the other; tried by the thermometer however, it will be found to be cooler ; or if it be applied to the other, it will at once be discovered to be below the tem perature of the hand that was not chilled.
Let us follow the effects upon common sen sation produced by a change of climate of an opposite kind. When the inhabitants of cal countries visit the hotter regions of the globe, how do they contrive to endure the heat in the first instance? Experience has often shown that when they are of the same race, they endure it at first with even greater case than the natives themselves, and that they brave with greater hardihood and less suffering the utmost ardour of the sun. This capacity of resistance, how_ ever, has its term, and those who possess it gradually lose it, as has been shown in a former passage of this article. The native of the colder clime is more robust, and his nervous system, less impressible, resists painful sensa tions in a greater degree, and is not over whelmed by the first effects of noxious influ ences. This conclusion is also susceptible of demonstration by the way of direct experiment. If during summer a frog be completely im mersed in a small quantity of water at the ordi nary temperature of this season of the year, and the same experiment be repeated during winter with water heated to the summer pitch, the animal will live much longer in the latter than in the former instance. The nervous sys tem of the animal, by the continued action of the cold of the autumn and winter, has been rendered much more capable of resisting noxi ous influences, as we have had occasion to see already. It is on the same principle that the Finlander, according to the account of Acerbi, can endure a bath at a much higher tempera ture than it could be borne by a native of a warm or more temperate climate.