HIBERNATION OF THE BATS. 115 



not afford a subsistence to the bats or swallows. The latter creatures meet the difficulty by 

 emigrating to more genial lands, and there finding the food which they would lose in these 

 cold climes ; but the former are obliged by the laws of their being to remain in the country 

 where they were born. It is evident, therefore, that unless some provision were made for 

 them during the insectless time of year, every bat would perish of hunger. 



Such a provision exists, and exerts its power by throwing the bats into a deep lethargy, 

 during which they require no food and take no exercise, but just live throughout the winter 

 in a state of existence that seems to partake more of the vegetable than the animal life. 



During hibernation, the respiration ceases almost wholly, and if it takes place at all, is so 

 slight as to defy investigation. The air in which these creatures pass the winter seems to 

 undergo no change by the breath, as would be the case if only one inspiration were made ; 

 and, strangest of all, the animal seems capable of existing for some time in gases that would 

 be immediately fatal to it in the waking state, or even without any air at all. The tempera- 

 ture, too, sinks to that of the surrounding atmosphere, although, as a general fact, the animal 

 heat of these creatures is rather high, as is the case with most flying beings, whether mammals 

 or birds. 



Many curious and valuable trials have been made upon bats while in a state of torpidity, 

 the subjects of experiment being placed in such a manner that the least act of respiration 

 made itself clearly visible, by the movements of a delicate index. The wing was extended 

 in such a manner, that the circulation of the blood was perceptible through its semi-trans- 

 parent membrane, and a thermometer was arranged so as to register the temperature. 



Very great care is requisite in conducting these experiments, because the least excitement, 

 or the slightest raising of the temperature, suffices to rouse the somnolent animal, and to alter 

 the conditions which are absolutely necessary for true hibernation. A hasty footfall, or an 

 accidental tap given to the table on which the creature rested, would cause it to make several 

 respirations, and to recover sufficient vitality to raise the temperature, and to consume some 

 portion of oxygen from the air. The same animal which passed ten hours in a state of perfect 

 somnolence, without producing any perceptible effect on the oxygen contained in the atmos- 

 pheric air, consumed in a single hour more than four cubic inches of oxygen, when aroused 

 and lively. 



The curious subject of hibernation will be again noticed in connection with the various 

 animals such as the marmot, dormouse and others, which pass the cold months in a state of 

 torpidity. 



