MARSHALL HALL 



63 



betwixt the spinal nerves. For a decapitated frog, 

 if it be pricked, not only draws away the part that 

 is pricked, but also creeps and jumps ; which cannot 

 happen but by consent betwixt the sensory nerves 

 and the motor nerves. The seat of which consent 

 must needs be in the spinal cord, the only remain- 

 ing portion of the sensorium. And this reflexion 

 of sensory impressions into motor impressions is not 

 accomplished in obedience to physical laws alone — 

 wherein the angle of reflexion is equal to the angle 

 of incidence, and reaction to action — but it follows 

 special laws as it were written by Nature on the 

 spinal cord, which we can know only by their effects, 

 but cannot fathom with the understanding. But the 

 general law, whereby the sensorium reflects sensory 

 impressions into motor impressions, is the preserva- 

 tion of ourselves." 



It was not possible, in 1800, to go further, or to 

 put the facts of reflex action more clearly : but this 

 fine sentence gives no hint of the truth that guided 

 Marshall Hall — that the " consent and commerce " 

 of reflex action are to be found at definite points 

 or levels in the spinal cord ; that the cord no more 

 " works as a whole" than the brain. The great- 

 ness of Marshall Hall's work lies in his recognition 

 of the divisional action of the cord : he proved the 

 existence of definite centres in it, he discovered the 

 facts of spinal localisation, and thus foreshadowed 

 the discovery of cerebral localisation. In his earlier 

 writings (1832-33) he showed how the movements 

 of the trunk and of the limbs are only one sort of 

 reflex action ; how the larynx, the pharynx, and the 

 sphincter muscles, all act by the " consent and 



