722 THE CEREBELLUM 



nervous tissue. Very similar changes have been observed in men 

 deprived of sleep during a period of ninety hours. 1 



The desire to sleep most commonly manifests itself by drowsiness, 

 a general malaise, a heaviness and dryness of the eyelids, a difficulty 

 in keeping the attention fixed, and other symptoms. This initial 

 state soon gives way to a condition of unconsciousness during which the 

 cortex is at least moderately impervious to external and internal 

 stimuli. All volitional actions, therefore, cease, while the reflexes are 

 in part preserved, although greatly diminished in their intensity. 

 This shows that some parts of the central nervous system remain more 

 active than others and this is true even of the cerebral cortex, because 

 the motor center becomes inactive before the sensations have been 

 lost entirely. Thus, a person may have reached the state of muscular 

 flaccidity while still capable of receiving sensations of sound and touch. 



The sense-organs themselves are in part protected against stimuli. 

 The eyelids are closed and the eyeballs rolled far upward and inward. 

 The pupils are markedly diminished in size. The latter effect may be 

 explained in the same manner as the constriction resulting on near 

 vision, i.e., it may be said to find its cause in afferent stimuli set up in 

 consequence of the convergence of the eyes. The conjunctival mem- 

 brane becomes dry owing to a diminished secretion of lacrimal fluid, 

 and is thus rendered less responsive to stimuli. A similar diminution 

 in the sensitiveness is noted in the oral and nasal cavities. Their 

 mucous lining also exhibits a certain dryness as a result of diminished 

 secretion. The ears are protected by a relaxation of the conductors 

 of sound situated in the middle ear, i.e., the ear drum and ossicles. 



Sleep having set in, the respirations become slower and deeper and 

 are frequently accompanied by loud noises produced by the air as it 

 rushes across the relaxed fauces, uvula, and edges of the laryngeal folds. 

 In many cases the respirations assume a periodic character, a certain 

 number of them being separated from others by a distinct interval of 

 comparative rest. The frequency of the heart is greatly reduced; the 

 vascular channels are relaxed and the blood pressure lessened. From 

 these changes it may justly be inferred that the tissues have entered 

 upon a state of relative inactivity; their low oxygen requirement and 

 small output of carbon dioxid clearly betraying a decided reduction in 

 their oxidations. 



Changes in the Depth of Sleep. Although sleep lasts as a rule for 

 a certain number of hours, it does not retain the same depth through- 

 out this period. This has been shown by endeavoring to awaken a 

 person at different intervals by sounds of measured intensity. A pen- 

 dulum beating against a metal plate, or small lead balls falling upon a 

 metal surface, have usually been used for this purpose. 2 While in- 

 dividual variations are very common, the results show that the 

 intensity of sleep increases steadily until it reaches its maximum 



1 Patrick and Gilbert, Psychol. Review, iii, 1896. 



2 Monninghoff and Piesbergen, Zeitschr. fur Biologie, xix, 1883. 



