280 ANNUAL OF SCIENTIFIC DISCOVERT. 



wakefulness or to slumber is the condition of the nervous system. If 

 its functional activity be protracted, the vision gives way under the 

 exhaustion of the nervous powers. If the action of the mind be purely 

 intellectual, if the feelings be not excited under that action, the waste 

 sensorially suffered is to be repaired by sleep, and the sensation of 

 slumber becomes uncontrollable. The demand for sleep is the desire 

 to have it ; and whether the absence of sensorial impressions results 

 from the settling of the mind to rest, or whether it be that darkness 

 cuts off all stimulation from light, or silence conduces to repose, sleep is 

 induced by the cessation of all visual or emotional excitement. If the 

 mind be withdrawn from the consciousness of its own operations, or if 

 it be acted upon by a monotony that either wearies attention, or, dis- 

 tracting it, leaves the sensorial image without perceptive impression, 

 the result is slumber, or the nervous relaxation of sleep. 



When the mind divides itself between the thoughts and the emotions, 

 mental activity being unsuspendecl, and the feelings unappeased, the 

 restlessness of anxiety becomes the inquietude of wakefulness ; and, 

 though there be weariness of both heart and soul, tired nature remains 



^j * 



ungratified by the restoration of sleep. 



Having thus indicated the circumstances under which beings slum- 

 ber that combine an intelligent nature with a sensational one, let us 

 examine how insects sleep. When the senses are blunted to external 

 impressions, under the lessened excitability of the mind, and our ideas, 

 more confused than vivid, are carried beyond ourselves in time and 

 place, we instinctively lie down to repose. All the creatures organized 

 with eyelids close the eyes against the influence of light. The temper- 

 ature of the body sinks, owing to diminished nervous energy, and we 

 seek with soft things to rest upon, warm things to cherish us with heat, 

 and then we go to sleep. The lower animals instinctively do what we 

 do, though each accommodates itself differently. The horse will 

 sleep standing in the warm shelter of the stable, though it lies down in 

 the pasture ; the bird reposes perching, but with its head buried in the 

 feathers of the wing ; the serpent coils itself in a circle, or folds itself 

 into the smallest possible space ; the fish screens itself in the weeds, or 

 buries itself in the sand or in the mud of the stream ; the insect with- 

 draws from the scenes of its ordinary activity, and is in a state of som- 

 nolent rest, when it remains motionless. As the insect has no eyelids, 

 no external closure of the eye gives evidence of sleep. 



As all the physiological facts of sleep in the vertebrate animal coin- 

 cide with effects exhibited by the heart and brain, and as insects have 

 neither of these organic centres, then sleep cannot be induced by any 



lans. At a certain hour in the morning, the keeper of the birds places a lantern in 

 the orifice of the wall, made for the special purpose of darkening and illumining 

 the room. The dim light thrown by the lantern on the floor of the apartment in- 

 duces the ortolans to believe that the sun is about to rise, and they wake and greed- 

 ily consume the food upon the floor. The lantern is withdrawn, and the succeeding 

 darkness acting as an actual night, the ortolans fall asleep. During sleep, little of 

 the food being expended iu the production of force, most of it goes to the forma- 

 tion of flesh and fat. After the birds have been allowed to repose for one or two 

 hours, to carry on digestion and assimilation, the keeper again exhibits the lantern 

 through the aperture. The mimic daylight awakes the birds again; again they 

 rise and feed ; again darkness ensues, and again they sleep. The representative 

 sunshine is made to shed its rays four or five times every day, and as many nights 

 follow its transitory beams. The ortolans thus treated become like balls of fatin 

 a few days. 



