CONDITION OF THE BRAIN, ETC., DURING SLEEP. 749 



respiration could be estimated, noted, in twenty-four hours, that the subject of the observa- 

 tion, awake but in a condition of complete repose, appropriated sixty-seven per cent, of 

 the entire amount of oxygen of the twenty-four hours during the night, and thirty-three 

 per cent, during the day, while he eliminated fifty-eight per cent, of the entire amount 

 of carbonic acid excreted, during the day, and forty-two per cent., during the night. 

 When the subject of the experiment worked during the day, by turning a heavy wheel, 

 the appropriation of oxygen was thirty-one per cent, for the day, and sixty-nine per cent, 

 for the night ; and the elimination of carbonic acid was sixty-nine per cent, for the day, and 

 thirty-one per cent, for the night. According to these observations, the system stores up 

 oxygen at night for use during the day, at this time eliminating a relatively small quan- 

 tity of carbonic acid ; and, during the day, it excretes more carbonic acid than during 

 sleep, appropriating then a relatively small amount of oxygen. 



This theory of sleep seems to rest upon observations too restricted to be adopted 

 without reserve. It is stated, indeed, that the first experiments of Pettenkofer and Yoit 

 were not confirmed in other observations made upon the same person. It is hardly pos- 

 sible, with our present information, to assume that sleep is due simply to want of oxygen, 

 and it is more in accordance with well-established physiological facts to attribute it to a 

 necessity for the general regeneration of the nervous tissue, though into this, the neces- 

 sity for oxygen may enter as one element in the physiological repair. 



During sleep, nearly all of the functions, except those directly under the control of the 

 sympathetic nervous system, are diminished in activity. The circulation is slower, and 

 the pulsations of the heart are less frequent, as well as the respiratory movements. These 

 points have already been considered under the heads of circulation and respiration. "We 

 have but little positive information with regard to the relative activity of the processes 

 of digestion, absorption, and secretion, during sleep. The drowsiness which many per- 

 sons experience after a full meal is probably due to a determination of blood to the ali- 

 mentary canal and a consequent diminution in the supply to the brain. 



CHAPTER XXIII. 



SPECIAL SENSES-TOUCH, OLF ACTION, AND GUSTATION. 



General characters of the special senses Muscular sense (so called) Appreciation of weight Sense of touch Varia- 

 tions in tactile sensibility in different parts Table of variations measured by the aesthesiometer Connection 

 between the variations in tactile sensibility and the distribution of the tactile corpuscles Titillation Apprecia- 

 tion of temperature Venereal sense Olfaction Nasal fossae Schneiderian and olfactory membrane Physio- 

 logical anatomy of the olfactory nerves Olfactory bulbs Olfactory cells and terminations of the olfactory nerve- 

 fibres Properties and functions of the olfactory nerves Mechanism of olfaction Eelations of olfaction to the 

 sense of taste Reflex acts through the olfactory nerves Gustation Savory substances Eelations between 

 gustation and olfaction Taste and flavor Modifications of the sense of taste Nerves of taste Chorda tympani 

 Facial paralysis with impairment of taste Paralysis of general sensibility of the tongue without impairment of 

 taste Glosso-pharyngeal nerve (first division of the eighth) Physiological anatomy General properties of the 

 glosso-pharyngeal Relations of the glosso-pharyngeal nerves to gustation Mechanism of gustation Physiolo- 

 gical anatomy of the organ of taste Papillae of the tongue Taste-buds, or taste-beakers Connections of the 

 nerves with the organs of taste. 



OUK study of the nervous system thus far has involved simply motion and what is 

 known as general sensibility ; and almost all our positive knowledge of these properties 

 has been derived from experiments upon the inferior animals. As regards sensation, the 

 experiments have referred to impressions recognized as painful ; and we have seen that 

 these are conveyed to the centres by nerve-filaments, anatomically as well as physiologi- 

 cally distinct from those which convey to the contractile parts the stimulus that gives rise 

 to motion. As far as we have studied the sensory nerves, we have alluded to simple im- 



