CHAPTER V. 

 THE SPINAL CORD. 



SEC. 1. AS A CENTRE OR GROUP OF CENTRES OF 

 REFLEX ACTION. 



OF the several functions of the spinal cord perhaps the most 

 striking and important is that of carrying out reflex actions. As 

 we have already said, the spinal cord is par excellence the organ 

 of reflex action; in by far the greater number of the reflex move- 

 ments of the body, the centre is supplied by some part of the spinal 

 cord. We have already (Book i. Chap, in.) touched on the 

 general features of reflex actions, and elsewhere have incidentally 

 dwelt on particular instances ; we may therefore confine ourselves 

 now to certain points of special interest. 



Reflex movements are perhaps best studied in the frog and 

 other cold-blooded animals, where the phenomena are less ob- 

 scured by the working of the other so-called higher parts of the 

 central nervous system. They obtain however in the warm-blooded 

 mammal also, but in these special precautions are necessary to 

 secure their full development. 



In the frog the shock which follows upon division of the spinal 

 cord, and which, as we shall presently see, for a while inhibits reflex 

 activity, soon passes away; within a very short time after the 

 medulla oblongata for instance has been divided the most com- 

 plicated reflex movements can be carried on by the frog's spinal 

 cord when the appropriate stimuli are applied. With the mammal 

 the case is very different. For days even after division of the 

 spinal cord the parts of the body supplied by nerves springing 

 from the cord below the section exhibit very feeble reactions only. 



