658 



ANIMAL HEAT. 



ble to cooling in the ratio of the general relax- 

 ation of the muscles, and of the degree in which 

 each of them in particular is in a state of qui- 

 escence. This is what happens in sleep, of 

 which we shall speak by-and-bye. 



In the rise of temperature observed along 

 with muscular contraction, we have in the first 

 place only considered the action of the blood ; 

 but neither contraction of the muscles nor the 

 afflux of a larger quantity of blood could take 

 place without the nervous influence ; for it is 

 the will which determines the muscular contrac- 

 tion, and the will only acts through the me- 

 dium of the nerves which are distributed 

 to the muscles. From this consideration it 

 follows equally as from general relations pre- 

 viously exposed, that whatever lessens the 

 nervous influence will, likewise tend to reduce 

 the temperature. Here we are, then, reverting 

 to the two general conditions which we had 

 already found to be the most influential in ca- 

 lorification, namely, the arterial blood and the 

 nervous system. 



This examination of the relative tempera- 

 tures of the different parts of the body has led 

 us, by the immediate comparison of the super- 

 ficial and deeper layers, to the consideration of 

 the 



Influence of external temperature. An in- 

 ert or inanimate body of higher temperature 

 than the surrounding medium will of neces- 

 sity cool faster at its surface than in its internal 

 parts. A living body, likewise, having within 

 itself a permanent source of heat, which we 

 shall suppose equally distributed through it, 

 will lose more caloric from its surface than from 

 its interior. This loss will become apparent 

 by the cooling of the surface, so long as the 

 source of heat remains everywhere equal. If, 

 on the contrary, it be unequally distributed, 

 if it be greater towards the surface, so 

 as to compensate the greater loss which 

 takes place there, the surface will have 

 the same temperature as the interior. Without 

 such a supposition it were necessary that the 

 surface of the body should be lower in tem- 

 perature than the interior. This, indeed, is the 

 actual state of the case. The external parts of 

 living bodies are colder than the internal parts, 

 because on the one hand the focus of heat is 

 less, by reason of the nature of the component 

 tissues, and on the other because the loss of 

 heat there is greater. When the external tem- 

 perature falls, then the outer layers will tend to 

 sink in temperature also, and will, in fact, sink 

 so long as the internal source of heat remains 

 the same. This partial refrigeration will be 

 propagated internally, and the general tem- 

 perature will be lessened unless the economy 

 provides against such an occurrence by an in- 

 crease of activity in its calorific powers. 



The same reasoning is applicable to move- 

 ments of the temperature of bodies under 

 the influence of that of the air. Heat will be 

 propagated from without inwards, and will 

 raise the general temperature of the body, un- 

 le; s it lessens in the same proportion as it re- 

 ceives external temperature, that which it pro- 

 duces of itself. 



The consideration of the changes in the in- 

 tensity of the internal focus, in other words, in 

 the faculty of producing heat, and of the con- 

 ditions which determine these, is the most im- 

 portant point of all in the study of animal 

 heat, on account of the multitude of practical 

 applications which result from it. 



It is obvious from what has already been 

 said that there is an essential difference between 

 inert or inanimate and animate bodies subjected 

 to the influence of external temperature. The 

 temperature of the former depends solely oh 

 the general laws which regulate the propaga- 

 tion of heat, whilst the temperature of the 

 others is subjected to the influence of another 

 element, namely, the heat which they them- 

 selves produce. Did this element continue 

 fixed and invariable, it would be possible to 

 determine, by the application of the known 

 data of physics, what must be the temperature 

 of a living body under the influence of a given 

 external temperature. But if this element 

 varies, and the laws according to which it 

 varies are unknown, it becomes impossible to 

 predict in what manner the temperature of an 

 animal will be affected by that of the medium in 

 which it lives. It is only very lately, therefore, 

 that the temperature of man and warm-blooded 

 animals, with the exception of those that hy- 

 bernate, has been believed to continue unaf- 

 fected in the midst of extensive variations in 

 the temperature of the surrounding atmosphere. 



Variations in the temperature, of animal 

 bodies in a state of health, independently of 

 external temperature. Duly to appreciate the 

 inquiries that have been instituted in this direc- 

 tion, the first question to be asked is, whether 

 or not the temperature of the body presents 

 variations, although external conditions continue 

 the same, or nearly the same? The answer 

 here must be in the affirmative : the body 

 varies in temperature at different times, exter- 

 nal circumstances as to temperature continuing 

 nearly the same. This is apparent in the ob- 

 servations of Dr. John Davy instituted with 

 another view, but quite available here. We 

 perceive that the individual designated No. 1, 

 having a temperature of 37 8 (100 F.), when 

 the air was at 26, 4 (79 F.), had a tempera- 

 ture of only 37, 5 (99, 75 F.) when the air 

 was at 26 P , 7 (80 F.), that is to say, the same 

 person showed a third of a degree c. less of 

 temperature, when the air, instead of becoming 

 colder, had actually become warmer in the 

 same proportion. The temperature of No. 3 

 was 37, 2 (99 F.), when the air marked 25, 

 5 (78 F.), and on another occasion it was only 

 36, 9 (98 F.), when the air was 26 (79 F.) ; 

 in other words, the temperature of the body, 

 instead of rising, had actually fallen by 0, 7 

 cent., when that of the external air had risen 

 0, 9 cent. 



Influence of the natural temperature of the 

 air on that of the body. It must be obvious 

 from the facts of the last paragraph that the 

 influence of external temperature cannot be 

 appreciated without having recourse to means 

 of observation calculated to make variations 

 dependent on foreign causes to disappear. 



