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Show 40 THE PRINCIPijE OF CtrAP. I. without first communicating with those cells on which our consciousness and volition depend. It is probable that sneezing and coughing were originally acquired by the habit of expelling, as violently as possible, any irritating particle fron1 the sensitive air-passages. As far as time is concerned, there has been more than enough for these habits to have become innate or converted into reflex actions; for they are common to most or all of the hiaher quadrupeds, and must therefore have been first ac;uired at a very ren1ote period. Why the act of clearing the throat is not a reflex action, and has to be leai·nt by our chHdren, I cannot pretend to say; but we can see why blowing the nose on a handkerchief has to be learnt. It is scarcely credible that the movements of a headless frog, when it wipes off a drop of acid or other object from its thigh, and which movements are so well co-ordinated for a special purpose, were not at first per· formed voluntarily, being afterwards rendered easy through long-continued habit so as at last to be per· formed unconsciously, or independently of the cerebral hemispheres. So again it appears probable that starting "·as originally acquired Ly the habit of jumping away as quickly as possible from danger, whenever any of our senses gave us warning. Starting, as we have seen, is accompanied by the blinking of the eyelids so as to protect the eyes, the n1ost tender and sensitive organs of the body; and it is, I believe, always accompanied by a sudden and forcible inspiration, which is the natural prepa1·ation for any violent effort. But when a man or horse starts, his heart beats wildly against his ribs, and here it may be truly said we have an organ which has never been under the control of the will, rartaldng iu the ~ene~·al reflex ~oyements qt CHAP. l. SERVICEABLE ASSOCIATED HABITS. 41 the body. To this point, however, I shall return in a future chapter. The contraction of the iris, when the retina is stimulated by a bright light, is another instance of a movement, which it appears cannot possiblv have been at first vol~~ta1:ily performed and then fixed by habit; for the ll'Is ' lS not known to be uuder the conscious control of the will in any animal. In such cases some explanation, quite distinct from habit will have to be discovered. The radiation of ne~·ve-force fr01n strongly-excited nerve-cells to other connected cells as in the case of a bright light on the retina causin~ a sneeze, may pe1·haps aid us in understandin{)' how fl . 0 some re ex actions originated. A radiation of nerve-force of this kind, if it caused a movement tending to lessen the primary irritation, as in the case of the contraction of the iris preventinoo too much light fro1n falling on the retina, might afte~·wards have been taken advantage of and n1odified for this special purpose. It further deserves notice that reflex actions are in all probability liable to slight variations, as are all corroreal structures and instincts; and any variations wh1ch were beneficial and of sufficient importance, would tend to be preserved and inherited. Thus reflex actions, when once gained for one purpose, might afte~·wards be modified independently of the will or habit, so as to serve for some distinct purpose. Such cases would be parallel with those which, as we have ?ve~·y reason to believe, have occurred with rr1any Instincts; for although some instincts have been developed simply through long-continued and inherited habit, other highly complex ones have been developed ~hro~gh the preservation of variations of pre-existing lnst1ncts-that is, through natural selection. I have discussed at som~ little length, though as l |