SEC. 3. THE REFLEX ACTIONS OF THE 

 SPINAL CORD. 



§ 457. In the preceding portions of this work we have 

 repeatedly 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 

 conclusions 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 conversely 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 anything else, that the ' highest ' animals are differ- 

 entiated from those ' below ' them. When we compare a rabbit, 

 a dog, a monkey and a man, the differences in the vascular, 



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