674 



ANIMAL HEAT. 



the maintenance of life according to their re- 

 lations with the temperature. We have seen 

 that it is at the minimum of temperature that 

 the cold-blooded animals possess the greatest 

 tenacity of life, as regards the most essential 

 relation, in other words they are in the con- 

 dition the most favourable to enable them to 

 do without air ; at this point they are in a state 

 to live for the longest time without breathing. 

 It is obvious that here they must require less 

 air than under any other circumstances ; they 

 must necessarily require so much the less, as 

 their life will continue longer here than under 

 any other circumstances without any access of 

 air at all. It is, however, essential to appre- 

 ciate duly this fundamental relation, namely, 

 that at the lower limit of the scale of tempera- 

 ture mentioned, cold-blooded animals require 

 less air to live, and what is more, they con- 

 sume less air than under any other circum- 

 stances, and are even incapacitated from con- 

 suming more than they do. The minimum 

 temperature of this scale consequently is an 

 ind^x of the maximum of vitality or tenacity 

 of life, and at the same time of the minimum 

 of respiration. In the same proportion as the 

 temperature rises, the vitality or tenacity of 

 life declines, which makes it necessary that 

 this declension should be compensated by a 

 corresponding increase in their relation with the 

 air, in order that the vivifying influence of 

 this fluid may neutralize the deleterious effects 

 of the increase of heat. And this is what 

 actually happens. With the rise in tempe- 

 rature the sphere of activity of the respiration 

 extends, and the vivifying influence of the air, 

 which increases with the quantity of the fluid 

 consumed, compensates the successive decre- 

 ments in vitality or tenacity of life, dependent 

 on successive increments of temperature. We 

 shall therefore express in a very few words this 

 fundamental relation between the tempera- 

 ture of the air and the maintenance of life 

 among the invertebrate series of animals, a 

 relation entirely deduced from direct experi- 

 ment, which we can but refer to here, but 

 which we shall lay before our readers with all 

 the requisite details in our article on RESPIRA- 

 TION. The rise of temperature in the scale 

 from zero to 40 c. exerts upon the nervous 

 system of cold-blooded animals an action the 

 tendency of which is to diminish its vitality ; 

 the air, on the contrary, exerts a vivifying in- 

 fluence on this system. It becomes necessary, 

 therefore, to the maintenance of life that their 

 respective relations with the economy be such 

 that their effects compensate or counterbalance 

 each other. 



The principle relative to the influence of 

 temperature on the vitality of cold-blooded 

 animals just laid down, is applicable in every 

 particular to the changes experienced and the 

 phenomena presented by the hybernating tribes 

 among the warm-blooded series of animals. 

 Their vitality changes with the wane of the year, 

 i. e. under the influence of prolonged exposure 

 to cold, in the same manner They are then in 

 a condition to exist with a supply of air by so 

 much the less as this influence has been more 



intense and more protracted ; and precisely as 

 the cold-blooded tribes, if entirely deprived of 

 air in winter, they will live for a much longer 

 time in this deleterious position than they 

 would have done in summer. 



Influence of temperature on the vitality of 

 warm-blooded animals and of man in the 

 states of health and disease. 



These principles and considerations lead us 

 to examine what happens among warm-blooded 

 animals in the same circumstances. There being 

 great and manifold analogies between them and 

 the preceding tribe of animals, there must also 

 be some community in the application of the 

 principles laid down; but as they also differ 

 in many important respects, this application 

 must be correspondingly restricted. In the 

 first place, then, there is complete analogy 

 between the one and the other with regard to 

 the influence of the superior thermal limit on 

 the vitality of the nervous system. To seize 

 the analogy properly, it is however necessary 

 to regard the temperature which modifies this 

 system in each series, from a point of view that 

 is common to both. Whether the temperature 

 proceeds from without or from within, we may 

 presume that it will influence or modify the 

 nervous system in the same manner, if not 

 to the same degree, inasmuch as this system 

 presents differences. Warm-blooded animals 

 having in general a high temperature at all 

 seasons of the year, they must be compared 

 in this respect with cold-blooded animals in 

 the height of summer. On the one hand, heat 

 within certain limits tends to increase sensibi- 

 lity and motility ; warm-blooded animals, 

 therefore, with a few exceptions, which always 

 present a high temperature, constantly exhibit 

 also, with a few exceptions, a high degree of 

 sensibility and motility. The same thing can 

 only be said of the cold-blooded tribes during 

 the continuance of the warm weather. On the 

 other hand, again, high temperature tends to 

 lessen the vitality proper to the nervous system, 

 or the faculty of living without the agency of 

 the ordinary stimuli. This is also the reason 

 why, if respiration be interrupted among warm- 

 blooded animals at all times, and among cold- 

 blooded animals during the warmer seasons of 

 the year, they all perish alike speedily or nearly 

 so. The difference in the time that elapses 

 before life is extinct still depends on, or is in 

 relation with, the difference of temperature. 

 For in the hotter season of the year, cold- 

 blooded animals never attain the temperature of 

 the warm-blooded tribes, even in the most 

 burning climates of the globe. Their nervous 

 system will consequently have a higher degree 

 of vitality in the sense already indicated ; that 

 is to say, they will not perish so promptly in 

 summer under deprivation of air ; but if they 

 be immersed in water at the mean tempera- 

 ture of warm-blooded animals generally, which 

 is about 40 c. (104 F.), they will die as sud- 

 denly .(at least this is the case with those of 

 small size upon which the experiment has been 

 made) as the warm-blooded Vertebrata when 

 deprived of the contact of air. 



