208 OUT OF DOORS. 



measures the quantity of air consumed by the creature 

 contained within it. After remaining twenty-four hours 

 in this machine, scientifically termed a pneumatometer, 

 the index gave no sign. The animal was then slightly 

 disturbed, and in the space of nearly three hours con- 

 sumed about one cubic inch of oxygen. But when more 

 disturbed, and forced to move briskly, it consumed five 

 cubic inches in one hour. 



Although the respiration is thus checked, and the 

 lungs cease their labours, the heart continues to pulsate, 

 though slowly, making less than thirty beats in a 

 minute. So we have a most curious phenomenon, i.e., 

 blood constantly circulating through the system without 

 any respiration to renew its vitality, and without even 

 the reservoirs of air which are possessed by the reptiles. 



The reason of the long hibernation of the bats is 

 evident. They feed wholly on insects, which likewise dis- 

 appear during the winter months ; and if there were no 

 means of reducing the bodily functions to the lowest 

 ebb compatible with the retention of life within the 

 frame, the whole race of insect-eating bats would be 

 swept off the earth in a single winter. 



It is sufficiently remarkable that the animals which 

 hibernate on account of the absence of food should 

 belong to the two extremes of the vertebrate kingdom. 

 The squirrel and dormouse might lay up a store so 

 large as to afford an abundant supply throughout the 

 whole winter ; but the bat, feeding only on animal sub- 

 stances, could not do so, and would starve but for the 



