772 



HIBERNATION. 



left the animal in this situation, in a cold atmo- 

 sphere, to resume its lethargy. (See Jig. 306.) 



I could now quietly convey the animal ready 

 prepared, and place it in the field of the micro- 

 scrope without disturbing its slumbers, and 

 observe the condition of the circulation. 



In this manner 1 have ascertained that, 

 although the respiration be suspended, the cir- 

 culation continues uninterruptedly. It is slow 

 in the minute arteries and veins ; the beat of 

 the heart is regular, and generally about twenty- 

 eight times in the minute. 



We might be disposed to view the condition 

 of the circulation in the state of hibernation as 

 being reptile, or analogous to that of the batra- 

 chian tribes. But when we reflect that the re- 

 spiration is nearly, if not totally, suspended, 

 and that the blood is venous,* we must view 

 the condition of the circulation as in a lower 

 condition still, and, as it were, sub-reptile. It 

 may, indeed, be rather compared to that state of 

 the circulation which is observed in the frog from 

 which the brain and spinal marrow have been 

 removed by minute portions at distant inter- 

 vals, f 



In fact, in the midst of a suspended respira- 

 tion, and an impaired condition of some other 

 functions, one vital property is augmented. 

 This is the irritability, and especially the irrita- 

 bility of the left side of the heart. The left 

 side of the heart, which is, in the hibernating 

 animal, in its state of activity, as in all the 

 other mammalia, only arterio-contractile, be- 

 comes veno-contractile. 



This phenomenon is one of the most remark- 

 able presented to me in the whole animal king- 

 dom. It forms the single exception to the 

 most general rule amongst animals which pos- 

 sess a double heart. It accounts for the possi- 

 bility of immersion in water or a noxious gas, 

 without drowning or asphyxia ; and it accounts 

 for the possibility of a suspended respiration, 

 without the feeling of oppression or pain, 

 although sensation be unimpaired. It is, in a 

 word, this peculiar phenomenon, which, con- 

 joined with the peculiar effect of sleep in in- 

 ducing diminished respiration in hibernating 

 animals, constitutes the susceptibility and capa- 

 bility of taking on the hibernating state. On 

 the other hand, as the rapid circulation of a 

 highly arterialized blood in the brain and spinal 

 marrow of birds probably conduces to their 

 activity, the slow circulation of a venous blood 

 doubtless contributes to the lethargy of the 

 hibernating animal. 



I need scarcely advert to the function of 

 defecation. It has already been briefly noticed 

 under the head of sanguification, with which it 

 proceeds pari passu. 



Iff regard to the nervous system, I can only 

 repeat that sensation and volition are quiescent. 



* M. Prunelle observes, " En comparant le sang 

 de deux chauve-souris auxquelles j'avois ouvert les 

 carotides, a Tune pendant son engonrdissement et 

 a 1'autre dans Tetat de veille, j'ai trouve celui de 

 la derniere beaucoup plus vermeil." Annales du 

 Museum, tome xviii. p. 28. 



t Essay on the Circulation, pp. 136-141. 



In my memoir upon the subject of hibernation,* 

 1 committed an error relative to this subject. 

 But I am now satisfied that what I considered 

 to be evidences of an unimpaired sensibility, 

 were phenomena of the excito-motorykind. Thus 

 I have observed that the slighest touch applied 

 to one of the spines of the hedgehog immedi- 

 ately rouses it to draw that deep inspiration of 

 which I have spoken. The merest shake in- 

 duces a few respirations in the bat. The least 

 disturbance, in fact, is felt, as is obvious from 

 its effect in inducing motion in the animal. 



It is from the misconception on this point 

 that the error has arisen, that the respiration is 

 not absolutely suspended in hibernation. This 

 function has been so readily re-excited, that it 

 has been considered as appertaining to the state 

 of hibernation. 



As I have already stated, the cerebral func- 

 tions sleep, the true spinal functions retain their 

 wonted energy ; and if the respiration be nearly 

 suspended, it is because little carbonic acid, the 

 excitor of respiration, is evolved. 



In the midst of a suspended or partially sus- 

 pended respiration, the irritability of the mus- 

 cular fibre becomes proportionately augmented. 



The single fact of a power of sustaining the 

 privation of air, without loss of life, leads alone 

 to the inference that the irritability is greatly 

 augmented in the state of hibernation. This 

 inference flows from the law already stated, 

 and the fact is one of its most remarkable illus- 

 trations and confirmations. 



It might have been inferred from these pre- 

 mises, that the beat of the heart would continue 

 longer after decapitation in the state of hiber- 

 nation than in the state of activity in the same 

 animal ; an inference at once most singular and 

 correct. 



This view receives the fullest confirmation 

 from the following remarkable experiment : on 

 March the 9th, soon after midnight, I took a 

 hedgehog which had been in a state of uninter- 

 rupted lethargy during 150 hours, and divided 

 the spinal marrow just below the occiput; I 

 then removed the brain and destroyed the 

 whole spinal marrow as gently as possible. 

 The action of the heart continued vigorous 

 during four hours, when, seeing no prospect of 

 a termination to the experiment, I resolved to 

 envelope the animal in a wet cloth, and leave 

 it until early in the morning. At 7 o'clock 

 A.M. the beat of both sides of the heart still 

 continued. They still continued to move at 

 10 A.M., each auricle and each ventricle con- 

 tracting quite distinctly. At half-after 1 1 A.M. 

 all were equally motionless ; yet all equally 

 contracted on being stimulated by the point of 

 a penknife. At noon the two ventricles were 

 alike unmoved on being irritated as before; but 

 both auricles contracted. Both auricles and 

 ventricles were shortly afterwards unirritable. 



This experiment is the most extraordinary of 

 those which have been performed upon the 

 mammalia. It proves several interesting and 

 important points : 1. That the irritability of the 

 heart is augmented in continued lethargy in an 



* Phil. Trans, for 1832. 



