636 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



0.0555 sec , whilst with a powerful shock it was only 0.0471 sec. * The time 

 occupied in the performance of a. reflex act on the same side of the body as 

 that on which the irritation is applied is shorter than on the opposite side, 

 and the longer period required in the latter instance is termed the "period 

 of reflex conduction." This also becomes very short, or almost impercep- 

 tible, when the irritation applied is very strong. Exhaustion of the Spinal 

 Cord prolongs the duration of the " reflex time." The strength of the 

 stimulus has no influence on the rapidity of the conduction in peripheral 

 motor nerves. 



503. That the movements executed by the limbs of the lower animals, 

 when these are no longer connected by the Spinal Cord with the Encephalou, 

 but remain iu nervous connection with the Cord itself, do not take place 

 through the intermediation of sensation, might be supposed to be sufficiently 

 proved by the simple fact, that division of the Cord in Man, and hence by 

 inference in the lower auimals, reduces the parts below to a state of complete 

 insensibility. But, on the other hand, the very performance, by decapitated 

 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 it is 

 found to guide to truth, could not be disproved. Whatever experiments on 

 decapitated auimals were appealed to, in support of the doctrine that the 

 Encephalon contains 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 ; but these have 

 been met by the assertion, that in such conditions, sensations are felt, though 

 they are not remembered. It is difficult, however, to apply such an explana- 

 tion to the case of Anencephalous human infants (in which all the ordinary 

 reflex actions have been exhibited, with an entire absence of brain), without 

 supposing that the Medulla Oblougata is the seat of a sensibility which we 

 know that the lower part of the Spinal Cord does not possess; and of this 

 there is no evidence whatever. Experiments on the lower animals, then, 

 and observation of the phenomena manifested by apoplectic patients and 

 auencephalous infants, might lead to the conclusion that the Spinal Cord 

 does not itself possess sensibility, and that its reflex actions are independent 

 of sensation. At this conclusion, Unzer, Prochaska, Sir G. Blane, Flourens, 

 and other physiologists had arrived ; but it was not until special attention was 

 directed to the subject by Dr. M. Hall, that facts were obtained by which a 

 positive statement of it could be supported. For the question might have 

 been continually asked, If the Spinal Cord in Man be precisely analogous in 

 function to that of the lower Vertebrata, why are not its reflex phenomena 

 manifested, when a portion of it is severed from the rest by disease or injury? 

 The answer to this question is twofold. In the first place, simple division of 

 the cord with a sharp instrument leaves the separated portion in a state of 

 much more complete integrity, and therefore in a state much more fit for 

 the performance of its peculiar functions, than it ordinarily is after disease 

 or violent injury; and as the former method of division is one with which 

 the Physiologist is not likely to meet in Man as a result of accident, and 

 which he cannot experimentally put in practice, the cases in which reflex 

 actions would be manifested are likely to be comparatively few. But sec- 

 ondly, a sufficient number of such instances have now been accumulated, to 

 prove that the occurrence is by no means so rare as might have been sup- 

 posed ; and that nothing is required but patient observation, to throw a great 



