670 



ANIMAL HEAT. 



apt to retain it longer than it had done when 

 exposed to cold without any preparation of the 

 kind implied; it will resist impressions of cold 

 longer after exercise than it would after a state 

 of perfect quiescence ; the nervous system 

 has acquired new energy ; the economy is in 

 a condition to react with greater effect than 

 when depending on the process just described, 

 that, namely, which takes place independently 

 of the agency of the will. The repetition of 

 the effects that follow exercise taken at due in- 

 tervals, hardens the frame to such a degree that 

 the body at length acquires the power, by 

 means of the insensible and involuntary reac- 

 tion alone, to resist degrees of cold which it 

 could not have borne without the violent and 

 voluntarily induced reaction of active muscular 

 exertion. 



The different states of the body in the cir- 

 cumstances just referred to deserve special 

 attention, because they are reproduced in 

 others, where the cause not being apparent 

 they seem to be spontaneous, though they are 

 in fact, as we shall have occasion to see, under 

 the influence of an analogous cause. We sup- 

 pose that on the first exposure to cold during 

 rest, the reaction from the afflux of blood to 

 the capillaries is slight, and that the cold is 

 even sufficiently intense to produce an opposite 

 effect, that is, paleness of the part chilled. 

 To this symptom of the action of cold, shiver- 

 ing is superadded in various degrees of inten- 

 sity. If recourse be now had to exercise, this 

 state will last for a period long in proportion 

 to its intensity, until violent and prolonged mo- 

 tion have restored the temperature. If the 

 exercise be continued, the heat increases, and 

 even rises above its degree at starting ; in this 

 case it first restores the proper heat of the skin, 

 and then causes this tegument to assume a red 

 colour, which may become extremely intense. 

 To this second state succeeds a third, in which 

 the skin, which had hitherto been dry and un- 

 perspiring, becomes soft and finally bedewed 

 with moisture. Here, then, we have three 

 different states induced under the influence of 

 cold acting at first without opposition on the 

 part of the system, and then combated by 

 powerful and voluntary reaction. First, we 

 have coldness, paleness, and shivering ; secondly, 

 heat and redness; thirdly, moisture of the skin 

 and sweating. In making the application 

 here of what has been said above upon the 

 repetition of these acts, we perceive that at the 

 same degree of external temperature the effects 

 which at first, and under other circumstances, 

 would follow the impression of such a degree 

 of cold, may cease to be felt. This happens 

 from the constitution having improved under 

 the actions and their effects, which have been 

 detailed, and that it is in a state, with the 

 assistance of its own inherent powers of insen- 

 sible and involuntary reaction, to resist refrige- 

 ration. But do we not, when we strengthen 

 the constitution to such a pitch as enables it to 

 resist an influence which was a cause of incon- 

 venience to it previously, cure it of an infir- 

 mity ? It is obvious from what precedes that 

 the temperature of the body may be indiffe- 



rently affected, either by a great fall in that of 

 the air, or by an insufficient production of heat. 

 The temperature of the body tends to sink 

 equally when, producing a great deal of heat, 

 it is exposed to severe cold, or when, producing 

 little heat, it is exposed to a moderate warmth. 

 In either case the effects upon the economy 

 will be analogous without being identical. In 

 each case there will be a keen sense of cold 

 according to the depression of the external 

 temperature on the one hand, or the slightness 

 of the evolution of heat on the other. In the 

 latter case the insensible reaction will be ex- 

 tremely limited, as well as the voluntary reac- 

 tion, on account of the deficient energy. But 

 there are still resources within the economy. It 

 is then that the involuntary and violent reaction 

 of which we have already spoken takes place. 

 The circulation and the respiration increase in 

 rapidity spontaneously. In the case which we 

 havagust supposed, there will be certain series 

 of phenomena, analogous to those we have 

 described as occurring in the instance of a 

 strong individual exposed to the influence of 

 severe cold, who surfers from it at first, and 

 subsequently opposes and vanquishes it by 

 means of a violent and voluntarily superinduced 

 reaction. When the faculty of engendering 

 heat sinks to a certain term, there will be not 

 only a vivid sensation of cold even in summer, 

 but all the other consequences of exposure to a 

 low temperature, such as paleness, shivering, 

 &c.; by-and-by the involuntary reaction will 

 not fail to take place; the respiration and 

 circulation are accelerated, and end by restoring 

 the temperature, if the lesion of the calorific 

 power have not been too extensive, the skin 

 being first hot and dry, and subsequently hot 

 and moist. Here, consequently, we have the 

 three periods precisely as in the case previously 

 described : 1st, coldness, pallor, and shivering ; 

 2d, acceleration of respiration and circula- 

 tion, accompanied in the second period by dry 

 heat, and in the third by sweating. There is 

 therefore the strongest analogy in the two 

 cases. They resemble one another in the cha- 

 racter of the phenomena, and the order of 

 their succession. This is so obvious as merely 

 to require mention ; there can be no occasion 

 for more particular illustration. They have 

 also the strictest relationship in their causes, 

 without these, however, being identical. In the 

 first case the individual produces a great deal 

 of heat, but he cannot engender enough by the 

 ordinary and insensible reaction, in conse- 

 quence of which he has recourse to the violent 

 and voluntary reaction, which soon produces 

 the desired effect. In the second, the indivi- 

 dual produces little heat, and the economy 

 may suffer from this diminution of the calorific 

 faculty to the extent of finding itself incapable of 

 restoring a sufficient degree of heat by means of 

 a violent and voluntary reaction. The violent 

 and involuntary reaction then succeeds, and pro- 

 duces all the effects of that which is put into 

 play under the empire of the will. Nor is the 

 resemblance limited to immediate results. It 

 further extends to the remote and definitive 

 effect. For in either case the violent effort 



