CHAP, v.] NUTRITION. 821 



taken up out of proportion to the carbonic acid expired. Indeed, 

 it has been observed that a dormouse actually gained in weight 

 during a hibernating period; it discharged during this period 

 neither urine nor faeces, and the gain in weight was the excess of 

 oxygen taken in over the carbonic acid given out. 



As far as regards the other functions of the body all that can at 

 present be said is that the several fundamental activities of the 

 various tissues, though lowered, are still continued very much as 

 usual. The muscles and nervous elements are irritable ; indeed 

 the hibernating animal may be awaked though with difficulty by 

 adequate stimulation; and as an instance of the fundamental 

 similarity of the sleeping with the awake condition we may say 

 that the slowly beating heart can during hibernation be still 

 further slowed or be arrested by stimulation of the vagus nerve. 

 The essential feature of hibernation in fact is that external cold is 

 not resisted by the thermotaxic nervous mechanism, but lowers the 

 metabolism of all the tissues, and thus lowers the functions of the 

 whole body. When even in deep winter the hibernating animal 

 is exposed to adequate warmth, the increased temperature awakes 

 the tissues to increased metabolism, and the awakened animal 

 regains the bodily temperature and acquires all the powers which 

 it possessed in midsummer. 



Preparatory to the oncoming of hibernation the body lays up 

 unusually large stores of fat for the winter's expenditure. Many 

 hibernating animals possess a ' hibernating gland ', the cells of 

 which become loaded with fat in the autumn and lose it during 

 hibernation ; but in all cases the great store of fat is in the 

 adipose tissue generally. The liver of the hibernating animal, at 

 all events of the dormouse, contains a considerable quantity of 

 glycogen, which may be regarded as quite comparable to the 

 hepatic glycogen of the winter frog ( 455). The fat thus stored 

 up before the approach of winter serves as the main supply of 

 material for metabolism in the winter sleep. Since during the 

 whole hibernating period some amount, at least, of oxygen is 

 at the command of the tissues, we have no reason to think that 

 the metabolism of hibernation is fundamentally different from the 

 metabolism of ordinary life, or that the stored up fat suffers changes 

 and gives rise to energy in other ways than by the oxidation 

 which fat in an ordinary way undergoes in the body. Nevertheless 

 a detailed study of the metabolism of hibernation accompanied by 

 direct calorimetric observations would probably disclose interesting 

 results. 



