276 SPECIAL PHYSIOLOGY. 



ance of volitional impulses, may be completely destroyed by a certain 

 lesion, which nevertheless does not interrupt the transmission of reflex, 

 or excito-motor, impressions on its afferent nerves; and, further, that 

 the effects of such impressions, may be widely diffused through the 

 cord. It frequently happens that such reflex phenomena, after injury, 

 do not manifest themselves, or at first only feebly, but that subse- 

 quently they become stronger, when the effects of concussion, for 

 example, have passed off, though not so far as to restore the volitional 

 power. 



Reflex movements ordinarily have a special .object or design, and 

 are therefore said to be purposive; a character which, as we shall 

 frequently find, by no means implies that they are either accompanied 

 by sensation, or directed by the will. Most frequently, they may, in 

 general terms, be said to have a conservative object in the animal econ- 

 omy. Besides the example of reflex movements, performed through 

 the cord, exhibited in the hinder limbs of the frog, the spinal cord of 

 which has been divided, instances of reflex movements, performed 

 through the cord, may be adduced in the human subject, when un- 

 conscious, as in sleep, or under the influence of chloroform, or when 

 awake, in a state of disease, or even in health. The withdrawal of the 

 feet, when tickled during sleep, the flinching of a patient under chlo- 

 roform, from any cause of irritation applied to the surface, also the 

 involuntary raising of the foot, from the pricking of a needle, and 

 the sudden withdrawal of the hand, on which hot sealing-wax has fal- 

 len, are instances of involuntary reflex movement taking place under 

 different circumstances. In the two latter cases, conscious sensation 

 accompanies the reflex acts, which are therefore designated sensori- 

 motor; in the two former cases, there is a greater or less approach 

 towards a suspension of sensation; but it may not be wholly lost, 

 though the memory of it is not retained. In the first instance, that 

 of sleep, a similar difference of opinion may obtain, in the mode of 

 interpreting the phenomena, conscious sensation being held, on the 

 one hand, to be merely blunted, or, on the other, to be entirely sus- 

 pended. But there remains another set of examples, in which there 

 can be no doubt of the complete annihilation of sensation, and of all 

 its attendant consequences, although active reflex movements can be 

 produced by external or even internal stimuli. Thus, in injuries or 

 diseases which cause compression, laceration, or softening of the spinal 

 cord, to such an extent as completely to destroy both voluntary power 

 over the limb, and likewise all sensation in it, violent reflex move- 

 ments may be excited, in the so completely paralyzed limb, by the 

 application of stimuli to the extremities of the afferent nerves, as by 

 tickling, pricking, or electrifying the skin of the soles of the feet, 

 when a movement of withdrawal will take place, over which the patient 

 has no control, as he would ordinarily have, if the cord were sound, 

 and of which, as well as of the sensations which the stimuli are calcu- 

 lated to produce, he has no perception or consciousness whatever, 

 provided his eyes be closed. An instance is recorded by John Hunter, 

 of a man whose spinal cord was ruptured. Being asked, when his feet 

 were irritated, whether he could feel the irritation which excited them 



