HIBERNATION AND ALLIED STATES IN ANIMALS 107 



natural consequence, stamped themselves on living 

 things, plants as well as animals. Sleep, then, is essen- 

 tially a rhythmic diminution of the activities of all the 

 tissues, but especially of that one which controls all 

 others, the nervous. Ehythm seems to be at the basis 

 of all things organic and inorganic, but has not been 

 enough considered in our explanation of living cells. 

 It was long the custom to explain sleep by anaemia of 

 the brain, whereas the very anaemia was due to a con- 

 traction of the blood-vessels of the part, accompanied 

 by the diminution of the heart-beat, both of which are 

 periodical and dependent on the rhythm of the nervous 

 system itself. Of course, temporary anaemia of the 

 brain favours sleep, though it is not the essential 

 cause. As a natural consequence of the decline in the 

 activity of the great controller of the cell activities 

 (metabolism), i.e. the nervous centres, it is found that 

 all the functions of the body, without exception perhaps, 

 are diminished during sleep. Marshall Hall and others 

 since his time have shown that the gaseous interchange 

 in a hibernating animal is greatly lessened. This 

 diminished metabolism explains why the animal does 

 not require to eat, or but little. It explains the dimin- 

 ished excretions, etc., etc. 



This being understood, it is not surprising that 

 hibernating animals may be kept under water for long 

 periods as is the case with newly-born mammals, as 

 kittens and puppies, whose vital machinery as yet 

 works very slowly, which are, in fact, in a condition but 

 slightly more advanced physiologically than the uterine, 

 which is a sort of reptilian pre-natal state, as regards 

 the circulation, respiration, etc. 



As the metabolism of reptiles and amphibians is of a 

 much slower kind than that of mammals, it is not 

 surprising that their winter sleep is more profound ; 

 but it is to be observed that the change from their 



