FUNCTIONS OF THE SPINAL AXIS. 697 



tendency to winking, which is performed at short intervals by the contraction 

 of the Orbicularis muscle; this is evidently a Spinal action, capable of being in 

 some degree restrained (like that of respiration) by the will, but only until 

 such times as the stimulus (resulting perhaps from the collection of minute 

 particles of dust upon the eyes, or from the dryness of their surface in conse- 

 quence of evaporation) becomes too strong to be any longer resisted. Again, 

 we have in sleep or in apoplexy an example of this purely spinal action, un- 

 balanced by the influence of the will, which, in the waking state, antagonizes it 

 by calling the levator palpebrae into action. As soon as the will ceases to act, 

 the lids droop, and close over the eye in order to protect it; and if those of a 

 sleeping person be separated by the hand, they will be found presently to 

 return. Here, as in studying the respiratory and other movements, we are led 

 to perceive that it is the Brain alone which is torpid during sleep, and whose 

 functions are affected by this torpidity. As Dr. M. Hall very justly remarks, 

 "the Spinal system never sleeps;" it is constantly in activity; and it is thus 

 that, in all periods and phases of Life, the movements which are essential to its 

 continued maintenance are kept up without sensible effort. The closure of the 

 pupil against a strong light is another movement of the same protective tend- 

 ency. The channel through which that just named is performed is completed 

 by the first branch of the Fifth arid the Portio Dura of the seventh. The con- 

 traction of the pupil is immediately caused by the Third pair, or Motor Oculi, 

 as is easily shown by irritating the trunk of that nerve and observing the result ; 

 but the stimulus which excites it is conveyed through the Optic nerve. But 

 although the contraction of the pupil is usually in close accordance with the 

 sensation occasioned by the impression of light upon the retina, yet there is 

 evidence to prove that the sensation of light is not always necessary; for, even 

 when the sight of both eyes has been entirely destroyed by amaurosis, the regu- 

 lar actions have been witnessed in the pupil, in accordance with varying degrees 

 of light impinging on the retina. Such cases seem to indicate that the motion 

 results from an impression upon the retina, which impression, being conducted 

 to the Sensorium, ordinarily produces a sensation; but that even where no sen- 

 sation is produced, on account of a disordered state of the- part of the ganglionic 

 centre in which the Optic nerve terminates, if the central tract which connects 

 that nerve with the Third pair retain its integrity, a reflex action may be excited 

 through it, although no sensation intervene. The rarity of the occurrence is 

 easily accounted for, by the fact that in most cases of amaurosis, the disease lies 

 in the retina or in the trunk of the nerve, and thereby checks both its spinal 

 and its encephalic actions. Although we are not at present acquainted with any 

 similar protective movements, in the Human being, designed to keep the organ of 

 Hearing from injury, yet there can be little doubt that those which we are con- 

 stantly witnessing in other animals, possessing large external ears, are reflex 

 actions excited by the irritation applied to them. In regard to the Nose, we 

 find a remarkably complex action that of Sneezing adapted to drive off any 

 cause of irritation ( 555). The stimulus is conveyed, in this case, not through 

 the Olfactory nerve, but through the Fifth pair; so that it is not dependent 

 upon the excitement of the sensation of Smell. The act of Coughing, also, may 

 be regarded as of a protective character; being destined to remove sources of 

 irritation from the air-passages. Many of the automatic movements, performed by 

 the limbs of Frogs and other animals, when their connection with the brain 

 has been cut off, appear destined to remove these parts from sources of irritation 

 or injury ; and they may thus be rightly placed under the same category. 



725. The fact that sensation is very commonly associated with the reflex 

 actions we have been considering, being produced by the impression that excites 

 them," has led many to suppose that it necessarily participates in them ; a 

 doctrine which we have seen to be untenable. But the question not unnaturally 



