THE PRINCIPLE OF CHAP. I. il least use/4 as often as the same causes arise, which originally excited them in us through the volition. In such cases the sensory nerve-cells excite the motor cells, 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 irri- tating particle from 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 higher quadrupeds, and must therefore have been first acquired at a very remote period. Why the act of clear- ing the throat is not a reflex action, and has to be learnt by our children, 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 head- less 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 was originally acquired by 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 most tender and sensitive organs 14 Dr. Maudsley remarks (' Body and Mind,' p. 10) that "reflex movements which commonly effect a useful end may, under the changed circumstances of disease, do great mischief, becoming1 even the occasion of violent suffering and of a most painful death."