ANIMAL HEAT. 



679 



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 

 additional excitement, which thensuperinduces 

 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 suffer 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 be 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. \Ve 

 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- 

 peratures, 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 ease, 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. Well- 

 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 case 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 calorification, under the standard necessary 

 to the economy. Whenever 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 warm 

 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 10 or 12 c., the hand will by-aud- 

 bv 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 cold 

 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 ease 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 



