SEC. 3. THE REFLEX ACTIONS OF THE 

 SPINAL CORD. 



582. In the preceding portions of this work we have re- 

 peatedly seen that though we can learn much concerning the 

 working of an organ, or tissue or part of the body by studying its 

 behaviour when isolated from the rest of the body, all the con- 

 clusions thus gained have to be checked by a study of the 

 behaviour of the same organ or part, while it is still an integral 

 part of the intact body. All the several organs and tissues are so 

 bound together by various ties, that the actions of each depend on 

 the actions of the rest ; and to say that the life of each part is a 

 function of the life of the whole, is no less true than to say that 

 the life of the whole is a function of the life of each part. This is 

 especially borne in upon us, when we come to study the actions of 

 the central nervous system. We may, on anatomical grounds, 

 separate the spinal cord from the brain ; but when we come to 

 consider the respective functions of the two, we are brought face 

 to face with the fact that in actual life a large part of the work of 

 the brain is carried out by means of the spinal cord, and con- 

 versely the spinal cord does its work habitually under the influence 

 of, if not at the direct bidding of the brain. We may gain certain 

 conclusions by studying the behaviour of the spinal cord isolated 

 from the brain, or of parts of the spinal cord isolated from each 

 other; but we must be even more cautious than when we were 

 dealing with other parts of the body, and must greatly hesitate to 

 take it for granted that the work which we can make the spinal 

 cord or a part of the spinal cord do, when isolated from the brain, 

 is the work which is actually done in the intact body when the 

 brain and spinal cord form an unbroken whole. Moreover this 

 caution becomes increasingly necessary, when in our studies we 

 pass from the simpler nervous system of one animal to the more 

 complex nervous system of another ; for it is by the complexity of 

 their central nervous systems more than by any thing else, that 

 the ' highest ' animals are differentiated from those ' below ' them. 



