286 FUNCTIONS OF THE NERVOUS SYSTEM. 



clearly defined what the Brain does not do. By many, even in recent times, 

 the Spinal Cord has been considered as a mere appendage to the Brain ; but 

 the phenomena of its independent action render such an idea quite inadmis- 

 sible. These phenomena have been especially pointed out by Dr. M. Hall; 

 and it is mainly owing to his arguments, that Physiologists are now for the 

 most part agreed in the general fact, that the Spinal Cord constitutes a dis- 

 tinct centre, or rather a collection of centres, of nervous influence, and that 

 its operations are carried on through the nervous trunks with which it is con- 

 nected. It is further generally admitted that its functions are independent of 

 the will; and that they are in effect frequently opposed to those of the Brain, 

 which operates on the muscles, either by a volitional, or by an emotional 

 impulse. And lastly, its actions are always (except when excited by a physi- 

 cal irritation directly applied to itself) entirely of a reflex character ; that is 

 to say, the motor impulses which originate in it are not spontaneous, but re- 

 sult from the stimulus of impressions, conveyed to it by the afferent trunks, and 

 operating upon it, to use the expression of Prochaska, according to certain 

 "peculiar laws written, as it were, by nature on its medullary pulp." It is 

 not, however, universally admitted that these actions are independent of sen- 

 sation; and some eminent physiologists, among whom may be named Dr. 

 Alison, still hold that the intervention of sensation is necessary in the case 

 at least, of the ordinary associated movements, which have definite ends in 

 view, and follow one another in regular succession, as those of Respiration, 

 for an impression to give rise to that organic change in the Spinal Cord, which 

 shall terminate in a muscular motion.* It will be desirable, therefore, to con- 

 sider the evidence upon which the statement rests, that reflex actions are in- 

 dependent of sensation, though ordinarily accompanied by it. 



364. In the first place, then, it has long been well known that, in the 

 Human being, the Spinal Cord does not by itself possess, in the remotest 

 degree, the power of communicating sensory impressions to the mind; since, 

 when its lower portion has been severed from the brain by injury or disease, 

 there is complete anaesthesia of all the parts of the body, which derive their 

 nerves exclusively from it. Hence it might be inferred, that throughout the 

 Vertebrated classes, the spinal cord is equally destitute of sensibility ; and 

 that any movements produced by stimuli acting through it, are the results of a 

 physical, and not of a sensorial change. This inference, however, has been 

 disputed ; and, if unsupported by other evidence, it would not, perhaps, be 

 entitled to rank as an ascertained truth. The very performance, by decapi- 

 tated animals of inferior tribes, of actions which had not been witnessed in 

 Man under similar circumstances, has been held to indicate, that the spinal 

 cord in them has an endowment which his does not possess. The possibility 

 of such an explanation however unconformable to that analogy throughout 

 organized nature, which the more it is studied, the more invariably is found 

 to guide to truth could not be disproved. Whatever experiments on decapi- 

 tated animals were appealed to, in support of the doctrine that the brain is 

 the only seat of sensibility, could be met by a simple denial that the spinal 

 cord is everywhere as destitute of that endowment, as it appears to be in Man. 

 The cases of profound sleep and apoplexy might be cited, as examples of 

 reflex action without consciousness ; and these might be met by the assertion, 

 that in such conditions sensations are felt, though they are not remembered. 

 It is difficult, however, to apply such an explanation to the case of anence- 



* See Outlines of Physiology, 3d edit., 211. By many of the German Physiologists, also, 

 it is maintained that Sensation is a necessary link in the chain of reflex actions ; but as they 

 employ the term sensation in a sense which does not involve consciousness, it is obvious that 

 their dissent from Dr. Hall's views is chiefly verbal. 



