464 PHYSIOLOGY CHAP. 



during waking (Mosso, Vase hide and Vurpas). Fauo (1885), and 

 Ptumnio and Ferannlni (1888), noted an appreciable delay in the 

 vascular reflexes during sleep, that is, the vasomotor reaction time 

 is increased. 



The fall in body-temperature during sleep was known to 

 Hippocrates. But Haller correctly points out that in regard to 

 thermogenesis we must distinguish between physiological sleep 

 and that induced by narcotics. The thermometric observations by 

 Marie de Manaceine show that in sleep the axillary temperature 

 drops in summer to 36'45 C., in winter to 36'05 ; it is lowest 

 between midnight and 3 A.M. This nocturnal fall of temperature 

 is due to diminished katabolism and therefore to reduced thermo- 

 genesis during sleep. 



All these functional changes in the organs and systems of 

 vegetative life correspond to the depression of the metabolic 

 activities of the sleeping organism, or more exactly to a pre- 

 dominance of the anabolic or assimilative over the katabolic or 

 dissimilative processes. 



The changes in the organs of animal life during sleep are more 

 characteristic. 



In slumber we lose the use of our senses, but they do not all 

 fall asleep at the same time, nor do they all sleep in the same 

 degree. The " sleep " to touch is light, while gustatory and 

 olfactory stimuli take effect with more difficulty. Hearing, like 

 touch, is excited in most sleepers by slight stimulation ; it is the 

 last sense to succumb, whereas sight is the first that passes into 

 abeyance. The closure of the lids during sleep is due to fatigue of 

 the levator palpebrae muscles. The eyeballs are directed upward 

 and diverge, the pupils contract and dilate at the moment of 

 waking a /////o.s/.s and niydriasi* due to decrease or increase in 

 the tone of the vaso-constrictor nerves of the iris, rather than to 

 relaxation or spasm of their antagonist muscles (Gubler and 

 Langler). 



The diminution of sensibility, or sleep of the senses in 

 general, is due to inactivity of the cortical centres rather than to 

 alterations in the peripheral sense-organs. The latter, in fact, are 

 pervious to stimuli during sleep ; they may react to sounds or 

 noises, to light even through closed eyelids, and to contacts and 

 odours even in slumber. During sleep the excitability of the 

 cerebral cortex to experimental stimuli diminishes (Tarchanoff, 

 1894), as well as the tendon and cremasteric reflexes (Eosenbacli, 

 1879), the vascular reflexes (Patrizi, 1896), and the pupil re- 

 flexes (Berger and Loewy, 1898). 



The voluntary muscles are relaxed in physiological sleep, yet 

 they often carry out co-ordinated reflex movements, initiated by 

 tactile or painful sensations, as the sting of an insect, or a cramped 

 position, etc. Again, apart from somnambulism, which is an 



