HIBERNATION. 



765 



respiration is inversely as the degree of irritabi- 

 lity of the muscular fibre, the former being 

 marked by the quantity of oxygen consumed in 

 a given time, ascertained by the pneumatome- 

 ter,* the latter by the force of galvanism neces- 

 sary to demonstrate its existence. The bird 

 tribes have a high respiration and a low irrita- 

 bility ; the reptiles have a high degree of irrita- 

 bility and little respiration. This law obtains 

 not only in the different tribes of animals, but 

 also in the different stages or states of the same 

 individual, the structural changes from one 

 stage to another being always a change from a 

 lower to a higher respiration, and from a higher 

 to a lower degree of irritability, and the change 

 of state, a change in the opposite direction : 

 thus the changes from the egg to the bird, from 

 the tadpole to the batrachian form, from the 

 larva to the chrysalis and the insect condition, 

 are changes in which, whilst a due ratio is con- 

 stantly maintained, the quantity of respiration 

 is augmented and the degree of irritability 

 diminished; on the other hand, the physiolo- 

 gical changes in the degree of activity in ani- 

 mals, during sleep, for example, but especially 

 in that remarkable change which is the subject 

 of this article, the respiration is diminished 

 whilst the degree of irritability is, pari passu, 

 augmented. 



On what this susceptibility of change de- 

 pends, and especially on what the power of 

 taking on an augmented irritability depends, is 

 at present unknown. But 1 think I may affirm 

 that it is upon this power that the capability of 

 passing into the state of hibernation reposes. I 

 suppose that all animals have the faculty of 

 sleeping ; during sleep the respiration is slightly 

 diminished, the irritability probably proportio- 

 nately augmented probably one ultimate ob- 

 ject of this state of repose ; but the phenomenon 

 has its appointed limit which it cannot pass. 

 In certain animals, that limit is not so con- 

 fined, the quantity of respiration is still further 

 diminished, the degree of irritability still further 

 augmented, and the deeper sleep, or lethargy, 

 of hibernation takes place. 



During this lethargy, the law of the inverse 

 ratio of the respiration and of the irritability 

 still prevails, and the animal merely puts on a 

 reptile state in these respects. Were the respi- 

 ration to be diminished without the appointed 

 augmentation of the irritability, the heart would 

 cease to be stimulated, and the animal would 

 die, as in the cases of torpor and slow asphyxia; 

 were the respiration augmented without the 

 proportionate diminution of the irritability, the 

 heart would be over-stimulated, and death 

 would alike ensue, as in the case of a hiberna- 

 ting animal too suddenly roused from its lethar- 

 gy, and as (probably) in the case of an animal 

 placed in pure oxygen gas. 



The difference between the hibernating and 

 all other animals then is, an ultimate faculty of 

 assuming an augmented degree of irritability of 

 the muscular fibre a power possessed by all 

 animals within certain limits, but by the hiber- 

 nating animal beyond the usual limit. 



See Phil. Trans, for 1832, p. 323. 



Sleep, however inscrutable in itself, is the 

 connecting link between the two physiological 

 states ; a disquisition on hibernation is, there- 

 fore, a disquisition on sleep on profound sleep. 

 It will shortly appear that one eminent philoso- 

 pher has fallen into the error of assimilating 

 different physiological phenomena by neglect- 

 ing to take this fact into his consideration. 

 Sleep and hibernation are similar periodical 

 phenomena, induced by similar causes, leading 

 to similar effects, and differing only in degree. 

 Hibernation appears more extraordinary only 

 because less familiar than sleep. Most animals 

 are, in fact, naturally awake and asleep every 

 revolving day, some being diurnal, others noc- 

 turnal. But in summer the bat actually hiber- 

 nates, loses its respiration, and with its respira- 

 tion its temperature, acquires vastly augmented 

 irritability, and presents the other phenomena 

 of complete hibernation, regularly and periodi- 

 cally every twenty-four hours; and the hedge- 

 hog and the dormouse present similar pheno- 

 mena, only after other intervals. 



Sleep then is the first stage of hibernation. 

 The faculty of passing into the second is iden- 

 tical with that of assuming a greatly augmented 

 irritability of the muscular fibre. Such are the 

 results of my long attention to this interesting 

 physiological question. Much error has arisen 

 from viewing hibernation as a simple effect of 

 cold. The influence of cold in inducing hiber- 

 nation is merely its well-known influence in 

 inducing sleep, concurring with the other causes 

 of this condition. The direct effect of cold on 

 the animal frame is, as I shall shortly have 

 occasion to state particularly, totally different 

 from hibernation. Hibernation is a physiolo- 

 gical condition ; the direct effect of cold, or 

 torpor, is, on the contrary, a pathological and 

 generally a fatal one. 



The term hibernation has usually been ap- 

 plied to designate what its etymology implies, 

 the condition in which certain animals pass the 

 winter season. An error is, as I have already 

 stated, involved in this view of the subject; for 

 the condition termed hibernation is not con- 

 fined to the winter season. Cuvier observes, 

 in speaking of the Tenrecs, " ce sont. des ani- 

 maux nocturnes qui passent trois mois de 

 1'annee en lethargie, quoique habitants de la 

 zone torride. Burguiere assure meme que c'est 

 pendant les grandes chaleurs qu'ils dorment."* 

 Hence the term Sommerschluf employed in Ger- 

 many. It is plain too, from this circumstance, 

 that the state of hibernation is not necessarily 

 connected with a low degree of external tempe- 

 rature, and we are surprised to find this cele- 

 brated naturalist, whom I have just quoted, 

 observing, " la seule condition de la lethargie 

 est le froid et 1'absence des causes irritantes." f 



I must repeat that hibernation is, in every 

 respect, but the parallel of ordinary sleep, vary- 

 ing only in force and duration. It is equally 

 marked by an inexplicable periodicity; it is 

 equally modified by cooperating or opposing 



* Regne Animal, ed. 1829, t. i. p. 125. 

 t Histoire des Sciences Naturelles, 1829. t. i. 

 p. 280. 



