502 COMPARATIVE PHYSIOLOGY. 



It is a matter of common experience that weariness, or the 

 exhaustion following on pain, mental anxiety, etc., is favorable 

 to sleep. 



A good deal of light is thrown on this subject by hiberna- 

 tion, particularly in mammals. 



From special study of the subject we have ourselves learned 

 that, however temperature, and certain other conditions may 

 influence this state, it will appear at definite periods in defiance, 

 to a large extent, of the conditions prevailing. Hibernation, 

 we are convinced, is marked by a general slowing of all of the 

 vital processes in which the nervous system takes a prominent 

 part. Sleep and hibernation are closely related. In both there 

 is a diminution of the rate of the vital processes, as shown by 

 the income and output, measured by chemical standards, with 

 of course obvious physical signs, as slowed respiration, circula- 

 tion, etc. While sleep, then, is primarily the result of a rhyth- 

 m.ical retardation of the vital processes, especially within the 

 nervous system, it is like hibernation in some degree (in the 

 lowest creatures, without a nerve system) the outcome of that 

 rhythm impressed on every cell of the organism aud the influ- 

 ence of which is felt in a thousand ways, that no doubt we are 

 quite unable to recognize. 



Hypnotism. — By the help of the above principles the sub- 

 ject of hypnotism, now of absorbing interest, may be in great 

 part explained. This condition is characterized by loss of vo- 

 lition and judgment. It may be induced in man and certain 

 other animals by prolonged staring at a bright object, assisted 

 by a concentration of the attention on that alone, as far as pos- 

 sible, combined with a condition of mental passivity in other 

 respects. The individual gradually becomes drowsy, and finally 

 fallls into a state in many respects strongly resembling sleep. 



Hypnotism proper may be combined with catalepsy, a con- 

 dition in which the limbs remain rigid in whatever condition 

 they may be placed. Modifications of the vascular and respira- 

 tory systems occur. Various animals have been hypnotized, as 

 the fowl, rabbit. Guinea-pig, crayfish, frog, etc. This condi- 

 tion is readily induced in the common fowl, more especially . 

 the wilder individuals, by holding the creature with the bill 

 down on a table and the whole animal perfectly quiet for a 

 short time. Upon the removal of the pressure the bird re- 

 mains perfectly passive and apparently asleep for some little 

 time. 



