672 



ANIMAL HEAT. 



18 (64, 5 F.), the temperature of the hedge- 

 hog was lower by 2 c., that of the marmot by 

 5, 25 c., and that of the dormouse by 5, 5 c. 

 than it had been at the previous date. This is 

 a considerable depression, if it be remembered 

 that the decline in the atmospheric temperature 

 was by no means considerable; that the air was 

 in fact still at a point which made it be felt as 

 warm to the generality of persons. The same 

 individual animals examined on the 7th of 

 November, the atmospheric temperature being 

 7, presented the following state. The mar- 

 mot had lost 9, 25 c., the dormouse 15, 5 c., 

 and the hedge-hog 21, 25 c. of their respec- 

 tive temperatures during the month of August, 

 so that their absolute temperatures were now 

 as follows: that of the marmot 27 (81 F.), 

 that of the dormouse 21 (70 F.), and that of 

 the hedge-hog 13, 75 c. (57 F.). Here, there- 

 fore, we have several warm-blooded animals 

 which in autumn approach very closely to the 

 cold-blooded tribes with regard to their calorific 

 power. 



If they be next observed during the period 

 of sleep, the relationship will be observed if 

 possible in a more striking degree. If, during 

 the state of watching, they suffer such a loss of 

 temperature as has been specified with the 

 gradual decline of the temperature of the year, 

 they will certainly suffer still more remarkable 

 changes during the state of sleep, in conformity 

 with the principles already fully developed. 

 The sleep of these animals will also become 

 longer and deeper in proportion as the nervous 

 system loses its power, under the influence of 

 the external cold, a loss which will be mani- 

 fested by a farther retardation in the motions of 

 circulation and respiration. But what is the 

 increasing weakness of the nervous system 

 during sleep but a more or less marked state 

 of torpor ? The same degree of cold con- 

 tinuing, or the degree of cold becoming gra- 

 dually greater, the disproportion as regards the 

 animal will increase also, and will necessarily 

 attain a term at which the torpor during 

 sleep will become lethargic. If the external 

 temperature goes on declining, and attains a 

 point at which it becomes dangerous to the life 

 of the creature, the cold, within certain limits, 

 ought to have the power of withdrawing the 

 animal from its state of lethargy. The excite- 

 ment which appertains to the waking period, 

 by accelerating the motions of circulation and 

 of respiration, will then cause the temperature 

 of the body to rise. But if the external tem- 

 perature does not become more favourable, or 

 if the animal finds no means of abstracting 

 itself from its influence, it has not sufficient 

 resource within itself and must perish. 



We have seen above that the changes in the 

 seasons produced great modifications in the 

 constitution of warm-blooded animals in gene- 

 ral. But it were difficult to imagine any greater 

 or more striking than those presented to us by 

 the species which we have just named, which 

 belong to the family of hybernating animals; 

 changes which arise from their passing the 

 winter months in a state of lethargy. When 



these animals are recalled from this state to- 

 wards the end of autumn, and during the 

 course of the winter, they may seem to resume 

 the characters which distinguish the vitality of 

 warm-blooded animals in general, but they are 

 in a very different state at this epoch from what 

 they are in summer. Their constitution has 

 un iergone important changes, which it is 

 necessary to examine and appreciate exactly. 

 These changes are inversely as those which the 

 most perfectly constituted warm-blooded ani- 

 mals experience. These, under the influence 

 of the increasing cold of autumn arid winter, 

 acquire new vigour, and their faculty of pro- 

 ducing heat increases in consequence. Those, 

 on the contrary, naturally much less energetic 

 even at the most favourable period of the year, 

 require to be excited and supported by the 

 high temperature of the summer or warmer 

 months, to permit them to exhibit all their 

 activity and strength. It is in the warm season 

 of the year that these animals have the greatest 

 degree of energy energy which has a certain 

 duration even after the external conditions 

 which have developed it have ceased to operate ; 

 for they have been as it were tempered by the 

 continuity of favourable circumstances, espe- 

 cially of the high atmospheric temperature. 

 This is the reason why they are so slightly 

 affected by the diurnal variations of the warm 

 season of the year; and even when this begins 

 to wane, and they are no longer stimulated by 

 the temperature proper to summer, they find 

 sufficient energy in the store accumulated, as 

 it were, during the fine season to enable them 

 to resist for a time and to a certain extent the 

 unfavourable influences with which they begin 

 to be surrounded. These continuing, however, 

 and even increasing, they gradually yield to 

 their influence, and sink lethargic, till revived 

 by the return of spring with its milder tempe- 

 rature. Their languor even augments not only 

 with a progressively lower degree of atmospheric 

 temperature, but with the persistence of a 

 degree which in itself is not by any means 

 excessive. 



These hybernating animals, whilst they pre- 

 sent the structure of the warm-blooded tribes 

 in general, still approach in a very remarkable 

 degree to the cold-blooded tribes in their 

 defective energy, or their indifferent powers of 

 reaction. This is to be regarded as the prin- 

 cipal source of the phenomena they exhibit in 

 the current of the year, phenomena which 

 are unknown among the more perfectly con- 

 stituted warm-blooded animals, but which are 

 absolutely of the same nature as those presented 

 by the cold-blooded Vertebrata in the same 

 circumstances, and which only differ in degree. 

 This analogy or resemblance in the phenomena 

 appears to arise from analogy not of structure 

 but of constitution. Very opposite organiza- 

 tions may have analogous constitutions ; cold- 

 blooded animals for example present the 

 greatest diversities of structure, and all are 

 affected and bear themselves in the same man- 

 ner under similar circumstances in very many 

 respects. They have thus a common constitu- 



