148 WALTER LOUIS HAHN. 



ing dog weighing 30 kilograms excreted 1.88 grams of fecal 

 matter per day. In the large number of bats which I have dis- 

 sected in winter, the stomach and upper part of the intestine was 

 always empty, although feces were present in the rectum. I am 

 convinced that the cave bats of southern Indiana seldom or never 

 eat during the winter, the stored fat being sufficient to sustain life. 



The degree of lethargy bears a close relation to the quantity of 

 superficial fat stored up by the animal and it is not related to the 

 temperature, either without or within the cave, nor to season. 

 In fact, the period of least activity is in the autumn and early 

 winter, before severe weather has begun. The bats are often 

 quite active in the cave during the cold weather of late winter. 

 Between August 8 and September 5, 1907, I took a number of 

 bats, Pipistrelhis snbflavus, Myotis iiicifiigus, and J/. siilntlaUis 

 from the caves to use in experiments. Some of these were very 

 fat while others were comparatively poor. On September 5 I 

 used two males of P. snhflaviis. The first one was quite poor 

 and flew readily when released in the room after being carried 

 for a short distance in a small box. The second bat had to be 

 prodded and tossed about before it could be awakened from its 

 lethargy sufficiently to fly. Even then its movements were more 

 sluggish and it struck obstacles oftener and also had to be 

 frequently disturbed in order to keep it in motion. I have never 

 seen a bat more difficult to arouse at any time during the win- 

 ter nor one more torpid when once induced to fly. An examina- 

 tion showed that this animal was exceedingly fat. This is not 

 an isolated case but merely illustrates what has been found sev- 

 eral times in this and other species. 



When in a state of lethargy, a bat cannot be quickly aroused. 

 Neither noise nor light appears to be a sufficient stimulus to 

 awaken it. Heat will arouse it more quickly than any other 

 stimulus and it will immediately draw away from the heat of a 

 candle. Mechanical stimuli are also effective and bats are some- 

 times aroused from torpor by being carried for a distance. Merz- 

 bacher ('03) found that the reactions of hibernating bats are 

 similar to those in which the cerebral hemispheres have been 

 destroyed. The clinging reflex is very evident, even in the most 

 torpid animals. In the torpid state the body temperature falls 



