678 



SLEEP. 



processes, and by which voluntary determina- 

 tions are formed. Impressions made upon 

 the organs of sense would seem only able to 

 act on the hemispheric ganglia through the 

 medium of the sensorium ; whilst the volun- 

 tary determinations, resulting from the exercise 

 of the reasoning powers, can only act on the 

 muscular system by the transmission of a 

 downward 'impulse from the hemispheric 

 ganglia to the automatic centres, in which the 

 motor nerves originate. 



If this be a true representation, the ordi- 

 nary phenomena of sleep are not difficult of 

 comprehension. The state consists essentially 

 in suspended activity of the sensorium, so 

 that impressions made on the organs of sense 

 are neither felt nor perceived, that is, 

 neither excite sensations, nor give rise to 

 ideas. In like manner, those automatic move- 

 ments which are dependent upon sensations for 

 their excitement are suspended; and as the tor- 

 por of the sensorium cuts off the functional 

 connection between the hemispheric ganglia 

 and the muscles, the latter cannot be called 

 into activity by any mental operations in 

 which the former may be concerned. In or- 

 dinarv profound sleep, the hemispheric ganglia 

 would seem to be in the same passive con- 

 dition as the sensorium itself; so that all 

 mental activity is suspended. In dreaming, 

 however, there is a train of ideas, called up 

 by the laws of association, and not regulated 

 bv any voluntary control, bespeaking a 

 partial activity of the hemispheric ganglia. 

 Into the conditions of this phenomenon we 

 shall inquire hereafter ; at present only ob- 

 serving, that if the sleep be deep, external 

 impressions are as completely unperceived by 

 the dreamer, as they are in a state of entire 

 unconsciousness ; and that, in like manner, 

 the strongest desire felt by the dreamer to 

 perform certain bodily movements, even 

 when he fancies that his life depends upon 

 them, is as ineffectual as if he were suffering 

 from a total paralysis. If external impressions 

 are in any degree felt by the dreamer, or his 

 volition can exert its power over the move- 

 ments of his body, the sleep is not profound, 

 but rather approximates towards the state of 

 somnambulism or sleep-waking, in which the 

 sensorial as well as the hemi.^pheric ganglia 

 are in a condition of partial activity. 



The state of simple sleep, again, is allied 

 to that of hibernation (see HIBERNATION) ; 

 the difference between them being essentially 

 this, that in the latter condition, besides the 

 profound torpor of the sensorial centres, 

 there is a great diminution or complete sus- 

 pension of the activity of the organic functions. 

 We may trace, in lact, every gradation be- 

 tween the simple repose of the sensorial cen- 

 tres, in which the state of sleep essentially 

 consists, to that complete suspension of all 

 the functions of life, which is of ordinary oc- 

 currence, during the winter season, in cold- 

 blooded animals. Many of these can even en- 

 dure the freezing process without the loss of 

 their vitality ; their activity being restored by 

 the renewal of warmth. Next to this is the 



condition of those hibernating mammalia, 

 which pass the winter in a state of uninter- 

 rupted torpor, and in which the organic func- 

 tions seem reduced to their lowest possible 

 amount of activity, short of entire stagnation. 

 This reduction is manifested in the slowness of 

 the circulation, the infrequency of the respira- 

 tory movements, the low degree of heat sus- 

 tained, the abatement of the demand for food, 

 and the small amount of carbonic acid, urea, 

 and other excretory products, set free during 

 the persistence of the hibernating state. But 

 there are other hibernating mammals, in which 

 the reduction is less decided, and the torpor 

 less profound ; these animals awaking from 

 their repose at long intervals, taking food from 

 the store which they have prepared, and again 

 relapsing into inactivity. And there are 

 others, again, in which it differs but little from 

 ordinary profound sleep, except that the pro- 

 portion of time passed in the waking state is 

 much less than usual. Further, it is a curious 

 observation of Dr. M. Hall's (loc. cit.), that 

 the ordinary diurnal sleep of certain hibernating 

 mammalia presents, in the reduced activity of 

 the organic functions, an approach to the tor- 

 por of their winter state. 



Sleep of Plants. The complete suspen- 

 sion of the organic as well as of the animal 

 functions during the hibernation of cold- 

 blooded animals corresponds with what has 

 been termed the winter sleep of plants. But 

 plants have also what has been called a 

 diurnal sleep ; and although it is obvious that 

 plants can present no phenomena really ana- 

 logous to those in which we have defined the 

 sleep of animals to consist, yet there are pe- 

 riodical changes in the condition of their leaves 

 and flowers which are deserving of consider- 

 ation under this head, especially as affording 

 ing an additional indication that even in the 

 functions of organic life there is a tendency to a 

 more or less decided alternation of activity and 

 quiescence. The parts of plants which exhibit 

 the changes in question, are the leaves arid the 

 Jloiuer&. In the former we frequently notice 

 an entire difference in the nocturnal and di- 

 urnal aspects of the leaves, which is the result 

 of a periodic change, affecting either the posi- 

 tion of the leaf as a whole, or that of the se- 

 veral leaflets of which a compound leaf is 

 formed. The petioles, or stalks of the leaves 

 or leaflets, either bend upwards or down- 

 wards ; so that the flattened surface of the 

 leaf is either elevated or depressed. This is 

 not a result of simple flaccidity ; for, as De 

 Candolle remarks*, the nocturnal position is 

 maintained with the same rigidity and con- 

 stancy as the diurnal; so that the " sleeping" 

 leaf would be broken, more readily than it 

 could be forced into the position which is 

 propel 1 to it during the day. Eleven different 

 mollifications are enumerated by the distin- 

 guished botanist just cited, in the manner in 

 which the leaves incline themselves to the 

 stalks on which they grow. Thus, of the 

 entire leaves which exhibit this phenomenon, 

 some sleep face to face, others back to back, 

 * Physiologic Yegetale, p. 855. 



