THE CEREBRO-SPIXAL NERVOUS SYSTEM. 485 



Reflex Action or Reflection. 



In man the spinal cord is so much under the control of the higher 

 nerve-centres, that its own individual functions in relation to reflex ac- 

 tion are apt to be overlooked; so that the result of injury, by which the 

 cord is cut off completely from the influence of the encephalon, is apt to 

 lessen rather than increase our estimate of its importance and individual 

 endowments. Thus, when the human spinal cord is divided, the lower 

 extremities fall into an} 7 position that their weight and the resistance of 

 surrounding objects combine to give them; if the body is irritated, they 

 do not move towards the irritation; and if they are touched, the conse- 

 quent reflex movements are disorderly and purposeless; all power of 

 voluntary movement is absolutely abolished. In other mammals, how- 

 ever, e. g. 9 in the rabbit or dog, after recovery from the shock of the 

 operation, which takes some time, reflex actions in the parts below will 

 occur after the spinal cord has been divided, a very feeble irritation being 

 followed by extensive and co-ordinate movements. In the case of the 

 frog, and many other cold-blooded animals, in which experimental and 

 other injuries of the nerve-tissues are better borne, and in which the 

 lower nerve-centres are less subordinate in their action to the higher, the 

 reflex functions of the cord are still more clearly shown. When, for 

 example, a frog's head is cut off, its limbs remain in, or assume a natural 

 position; they resume it when disturbed; and when the abdomen or back 

 is irritated, the feet are moved with the manifest purpose of pushing 

 away the irritation. The main difference in the cold-blooded animals 

 being that the reflex movements are more definite, complicated, and 

 effective, although less energetic than in the case of mammals. It might 

 indeed be thought, on superficial examination, that the mind of the ani- 

 mal was engaged in the acts; and yet all analogy would lead us to the 

 belief that the spinal cord of the frog has no different endowment, in 

 kind, from those which belong to the cord of the higher vertebrata: the 

 difference is only in degree. And if this be granted, it may be assumed 

 that, in man and the higher animals, many actions are performed as reflex 

 movements occurring through and by means of the spinal cord, although 

 the latter cannot by itself initiate or even direct them independently. 



Cutaneous and Muscle Reflexes. In the human subject two 

 kinds of reflex actions dependent upon the spinal cord are usually dis- 

 tinguished, the alterations of which, either in the direction of increase 

 or of diminution, are indications of some abnormality, and are used as a 

 means of diagnosis in nervous and other disorders. They are termed 

 respectively (a) Cutaneous reflexes, and (b) Muscle reflexes, (a) Cu- 

 taneous reflexes are set up by a gentle stimulus applied to the skin. The 

 subjacent muscle or muscles contract in response. Although these 

 cutaneous reflex actions may be demonstrated almost anywhere, yet cer- 

 tain of such actions as being most charactsristic are distinguished, e. g., 



