NATURAL HISTORY. 



847 



< ration ami circulation also gradu- 

 ally diminish, and they lose the 

 greatest part of their animal heat, 



I one of the most marked characters 



' of their class; in a word, their 

 life seems totally arrested ; all the 



' springs which retain or set in mo- 

 tion tlie elements of organization 

 seem to have lost their activity, 

 and yet life still remains, nay, may 

 be prolonged by that lethargy 

 beyond its natural limits: neither 

 death nor decomposition has taken 

 place ; and wlien the cold or other 

 accessaries of the lethargic state has 

 ceased, the animal awakes and re- 

 sumes its usual functions. 



When the class proposed, in 

 J 799, that naturalists should con- 

 sider in detail the circumstances 

 which produce, accompany, and 

 put an end to the lethargic state, 

 it was not expected that a com- 

 plete solution of the point would 

 be obtained, but merely that the 

 attention of naturalists, when di- 

 rected to so great an object, might 

 throw some light on it. 



The most important memoirs on 

 this subject have appeared in Spal- 

 lanzani's posthumous Treatise on 

 Respiration, published in 1803, 

 and in 1807, by his friend M. 

 Sennebier. M. Mangali, the pupil 

 and successor of Spallanzani pub- 

 lished, some experiments at Pavia, 

 on the same subject, and Mr. Car- 

 lisle in the Philosophical Transac- 

 tions for 1803, has thrown much 

 light on the question, although we 

 are not )ct perhaps able to solve 

 the question. 



Messrs. Herholdt and Rafn, of 

 Copenhagen, M. Saissy, a physi- 

 cian of Lyons, and M. Prunelle of 

 Montpcllier, have successively pre- 

 sented memoirs of great merit to 



the Institute, on the torpidity of ani- 

 mals; and we think it right to give 

 here a detail of some of the pliKno- 

 mena, with some hasty conjectures 

 respecting the cause. 



Cold is the most necessary acces- 

 sory to sleep ; but it is not the only 

 one ; there must also be an absence 

 of irritating causes, such as noise, 

 food, ilc. Several of these animals, 

 when domesticated, do not sleep, 

 notwithstanding the cold. An at- 

 mosphere deficient in oxygen is 

 also favourable, and frequently ne- 

 cessary. This is the reason that 

 most animals roll themselves up be- 

 fore falling asleep. 



The degree of heat, although va- 

 riable according to the kind of ani- 

 mal and accessory circumstances, 

 is always a little higher than the 

 freezing point ; a too violent cold 

 lias the effect of awakening ani- 

 mals when they are suddenly expos- 

 ed to it. 



Quadrupeds subject to lethargic 

 sleep, have not in general their blood 

 colder than other animals in the or- 

 dinary state, nor do they consume 

 less oxygen in respiration ; it ap- 

 pears, however, that their heat de- 

 creases a little with that of the at- 

 mosphere, although it always re- 

 mains suHiciently liigh while they 

 are awake. 



When once asleep, their breath* 

 ing and circulation become slower, 

 the consumption of oxygen de- 

 creases in the same proportion; 

 they lose all feeling when the le- 

 thargy is at its height. Irritabi- 

 lity seems to be the function which 

 is best preserved. 



Their animal heat decreases in 

 the same interval to one or two 

 degrees above (Reaumur), but 

 it docs not become lower ; and if 



wc 



