452 BIOLOGY. 



2752. The first cause resides in the want of stimulus. 

 The nerves of the senses are not polar, do not therefore 

 excite the brain, nor does this again affect the motor 

 system. The muscle therefore arrives at a state of non- 

 tension ; it becomes relaxed, and along with it necessarily 

 the organs of sense, which are thrown into activity by 

 muscular motion. The arms and fingers, whose business 

 is to touch, sink down; the feet which move, and 

 thereby warm and animate the body, are slackened and 

 bent together; the body is in the recumbent posture; 

 the eyelids drop, the light no longer plays upon the 

 visual organs, the external and internal auditory muscles 

 flag also, and the sound is no longer borne upon the ear. 

 Now also does the tension of the senses with the brain 

 cease, and with it the sensation there is sleep. 



2753. This sleep arising from want of stimulus is a 

 faint sleep, and rendered useless by dreams. For there 

 is actually no cause present why the encephalic tension 

 should entirely cease. Men, who do not fall asleep 

 through fatigue, but from want of work, sleep restlessly, 

 awake easily, and again readily fall asleep. Their life is 

 dreaming. 



2754. The other cause of the polar suppression in the 

 nerves is like that of the extension of the muscles, or 

 their falling to sleep ; it is thus the discharge of the too 

 strongly excited poles. With too high a degree of fibrous 

 tension, which also originates through too long a con- 

 tinuance of the tension, the fibre is placed in a state of 

 activity, which consists in the antagonism being balanced 

 by approximation of the ends. Were nerves, when 

 greatly tensed, capable of being shortened, they would 

 also discharge themselves, and come at least for one 

 instant to rest they would sleep. 



2755. The falling asleep of the fibre is its sleep, 

 though it also does not last long. So is the expansion 

 of the heart its sleep, so is expiration the sleep of the 

 thorax. 



2756. In all polarizable organs there is a change or 

 alternation of waking and sleeping, which endures a 

 longer and shorter time. This periodicity depends upon 



