THE ORGANS 21 



lost the power of standing upright under these circum- 

 stances, but they no longer retain any power of either feel- 

 ing what is going on in their legs, or, by an act of their 

 own will, causing motion in them. 



And yet, though the mind is thus cut off from the lower 

 limbs, a controlling and governing power over them still 

 remains in the body. For if the soles of the disabled feet 

 be tickled, though the mind does not feel the tickling, 

 the legs will be jerked up, just as would be the case in 

 an uninjured person. Again, if a series of galvanic .shocks 

 be sent into the spinal cord, the legs will perform move- 

 ments even more powerful than those which the will 

 could produce in an uninjured person. And, finally, if the 

 injury is of such a nature as not simply to divide or injure 

 the spinal cord in one place only, but to crush or pro- 

 foundly disorganise it altogether, all these phenomena 

 cease ; tickling the soles, or sending galvanic shocks along 

 the spine, will produce no eftect upon the legs. 



By examinations of this kind carried still further, we 

 arrive at the remarkable result that while the brain is the 

 seat of all sensation and mental action, and the primary 

 source of all voluntary muscular contractions, the spinal 

 cord is by itself capable of receiving an impression from 

 the exterior, and converting it not only into a simple 

 muscular contraction, but into a combination of such 

 actions. 



Thus, in general terms, we may say of the cerebro- 

 spinal nervous centres, that they have the power, when 

 they receive certain impressions from without, of giving 

 rise to simple or combined muscular contractions. 



6. Sensory Organs. — But you will further note that 

 these impressions from without are of »ery different char- 

 acters. Any part of the surface of the body may be so 

 affected as to give rise to the sensations of contact, or of 

 heat or cold ; and any or every substance is able, under 

 certain circumstances, to produce these sensations. But 

 only very few and comparatively small portions of the 



