7 88 A MANUAL OF PHYSIOLOGY 



(p. 840), but we cannot deny to the brain the possession of 

 reflex powers as well. The movements in which the only nerve 

 centres concerned are those of the spinal cord are above all reflex 

 (p. 796). But some of its centres, and especially those lying in 

 the medulla oblongata e.g., the respiratory centre are, much as 

 they are influenced by afferent impulses, capable of discharging 

 automatic impulses too. And while consciousness is certainly 

 bound up with integrity of the brain, and in all the higher 

 mammals is probably associated with cerebral activity alone, 

 it has been plausibly maintained that the spinal cord, even of 

 such an animal as the frog, is also endowed with something 

 which might be called a kind of hushed consciousness. If this 

 is so for the frog, with its distinct though relatively ill-developed 

 cerebral hemispheres, it must be still more likely in the case of 

 fishes and animals below them, which are practically devoid of 

 a cerebral cortex altogether. 



Functions of Spinal Cord (including Medulla Oblongata). 



The functions of the spinal cord may be classified thus : 



1. The conduction of impulses set up elsewhere either in 



the brain or at the periphery. 



2. The modification of impulses set up elsewhere (reflex 



action) . 



3. The origination of impulses (?). 



i. Conduction of Nervous Impulses by the Cord. The old 

 controversy as to whether the white fibres of the spinal cord 

 are directly excitable may be considered as definitely settled in 

 the affirmative. The inquiry was complicated by the presence 

 of the spinal roots, which, since the experiments of Charles Bell, 

 have been known to be capable of excitation by artificial stimuli. 

 But at length the difficulty was overcome in this way. The 

 posterior (dorsal) portion of several segments of the cord with 

 the attached posterior roots and the grey matter was excised. 

 Long strands of the white matter of the anterior (ventral) 

 portion of the cord were isolated, and laid on electrodes, and 

 contractions of muscles were seen to follow stimulation, even 

 when the anterior roots nearest the stimulating electrodes had 

 been cut, and every precaution taken to avoid escape of current 

 on to the distant anterior roots of the nerves supplying the 

 muscles. Indeed, apart from direct experimental evidence, 

 the fact that the white fibres of the brain are universally admitted 

 to be excitable by artificial means would be of itself almost 

 sufficient to decide the question, for we know of no essential 

 difference between the cerebral and the spinal fibres. But the 

 conditions must rarely occur under which direct stimulation 



