ZOOLOGY. 37- 







the hinder segment. Here was a case which would have been pronounced 

 very simple. Division of the cord had seemingly destroyed all power of 

 voluntary movement in the limbs below the section. The hind legs seemed 

 paralyzed. When the anterior segment was irritated, the animal crawled 

 away, dragging the motionless posterior segment after it. When this pos- 

 terior segment was irritated, the animal did not crawl, but simply withdrew 

 the limb or tail. If I touched the tail or hinder leg with acetic acid, the whole 

 of the posterior segment (in which volition was said to be destroyed) began 

 to move, and the legs set up the crawling action, attempting to push the 

 whole body forward, which could not be effected, because the anterior seg- 

 ment was perfectly motionless. The hind legs, which never moved when 

 the anterior segment was irritated, moved now in obedience to the spinal 

 volition ; and the anterior segment, which before seemed so energetic in its 

 voluntary movements, was now perfectly unmoved. Each centre rules its 

 own segment. If the motionlessness of the hind legs, when the animal 

 crawled, is a proof that voluntary power was destroyed in those legs, the 

 motionlessness of the fore legs when the hind legs moved is equally a proof 

 that voluntary power is destroyed in the fore legs. The real truth seems to 

 be that each segment has its own volitional centre, and that the one is never 

 affected by the other. I have, at this moment, a newt with the cord divi- 

 ded near the centre of the back. The operation was performed four days 

 ago, and the animal has so far recovered from it that no spectator could dis- 

 tinguish between the voluntary power of its two segments. When the flame 

 of a wax match is brought near the cerebral segment, the fore legs set to 

 work, and the animal crawls away, dragging the hinder segment along. 

 When the flame is brought near the spinal segment, the hind legs set to work, 

 and the body moves sideways, the anterior segment remaining perfectly 

 quiescent. All other stimuli produce similar results. I venture to submit 

 that the explanation here proposed of two independent volitional centres is 

 far more consistent with the phenomena than the explanation offered by the 

 reflex theory; unless the actions of the posterior segment of the newt are 

 evidences of sensation and volition, I know of no kind of evidence for the 

 existence of such properties in the cerebral segment. ... I will not occupy 

 the attention of this meeting with the recital of other experiments. Those 

 already cited suffice to indicate the nature of the evidence on which I found 

 my positions. And, indeed, I might rest on one simple fact as proof that the 

 spinal cord is a sensational centre, namely, the fact that whenever sensi- 

 bility is destroyed all actions cease to be coordinated. Every one present 

 knows how greatly our muscular sensibility aids us in the performance of 

 actions ; but it has apparently been forgotten that if sensibility be destroyed 

 in a limb, by section of the posterior roots which supply that limb, the power 

 of movement will be retained so long as the anterior roots are intact; but 

 the power of coordinated movement will be altogether destroyed. With 

 diminishing sensibility we see diminishing power of coordination, the move- 

 ments become less and less orderly ; and with the destruction of sensibility, 

 the movements cease to have their coordinated harmony. Now, in the cases 

 I have cited, it is clear that this power of coordinating movements some- 

 times very complex movements was nearly, if not quite, perfect in the 

 decapitated animal ; therefore, if coordination implies sensibility, the con- 

 clusion seems inevitable that the spinal cord is a centre of sensibility. The 

 whole case may be summed up thus : 1st. Positive evidence proves that, in 

 decapitated animals, the actions are truly sensorial. 2d. Positive evidence, 



