428 TEMPKRATUKE AND LIFE. 



lower. Horwatb has stated that tlie temperature of a hibernating 

 marmot reached 2°. As soon as warm weather returns they wake up, 

 become active, and their temperature becomes normal. They are much 

 leaner than before their winter's sleep, having lived for several months 

 on their own accumulation of fat. Here is an animal alternately warm 

 blooded and cold blooded in summer and winter. The cause of this 

 strange alternation has not yet been explained and is exceedingly com- 

 plicated. With them the thermic liroduction is relatively slight. It is 

 cold that determines the hibernal sleep, for it is easy to produce this 

 by subjecting the animal to prolonged cold by artiticial means. No 

 investigations to my knowledge have been made of the resistance of 

 this species of animals to heat. I mean to say, of the elevation of 

 internal temperature above the normal level of the summer, but it is 

 not to be supposed that their endurance would be as great as in case 

 of extremes of cold. 



This class of hibernating animals unite the heterothermic and home- 

 othermic si)ecies, and serve to show once again that everything in 

 nature is related. Sudden lenps are no longer held to exist in the phy- 

 siology of creatures which are similar in organic structure; science 

 finds everywhere transitions. 



Finally, all living organisms generate heat, more or less it is true, 

 according to their activity and their structure, but all produce it. In 

 the same manner all organisms submit to the influence of the surround- 

 ing atmosphere, although all do not follow the variations. For each 

 there is a degree of heat which is best adapted to its perfect develop- 

 ment. All die as soon as the external temperature reacts on the internal 

 temperature to such an extent that the latter is carried above or below 

 a certain jioint. The only difference is in the facility with which this 

 action of the external temperature operates upon the internal tempera- 

 ture of the organism. 



