Ccmscioiisn ess. 7 1 > 



feel it. There is nothing violent in the supposition that the whole sensi- 

 bility of the skin has been transferred to the brain, leaving only motor 

 reflex functions in the ganglions of the spinal cord. On the other hand 

 it is not inconsistent with the dynamic theory to suppose that some sen- 

 sibility still remains in the spinal ganglia, since, wherever the seats of 

 sensibilit}^ now are, they have been formerly diffused to various parts of 

 the body, and the question whether their removal to the brain, which has 

 gone on in the past and is no doubt still going on, is yet complete or 

 not, appears to me to be of subordinate importance. If we do not admit 

 the principle of differentiation and transfer at all, then we should have to 

 hold that sensibility still resides equally in all the tissues, which is ob- 

 viously not so. If we do admit it the conclusion follows tffat it may 

 all become transferred. 



It was observed above that sensation is motion in different tones, that 

 is, that unlike sensations are different rates of movement. This ap- 

 plies obviously to different tones that belong to the same character of 

 movement. But there may be two modes of molecular motion, the un- 

 dulatory like that of light, and the pulsatory like that of sound; so that 

 probably we may have two sensations at the same rate or pitch, totally 

 differing in character, as sound and warmth. There may be other pecu- 

 liarities in vibratory motion besides these,- which vary our sensations. 

 The senses of smell and taste and the muscular sense have peculiarities 

 which appear to require a different classification. 



The conditions which produce sensation are those consequent upon an 

 arrest of motion, and as motion cannot be quenched or annihilated, all 

 that is meant by " arrest " is its change from one form to another. The 

 differences that occur in sensations are due to differences in the form 

 of the motions arrested, and we have a vast number of sensations be- 

 cause there is an equally vast number of tones and various modes in 

 which bodies move. 



We often speak of heat being the result of friction and of being a 

 mode of motion. This is true, but the idea we usually associate with 

 the expression is decidedly mixed. The friction of two bodies rubbed 

 together produces a rise of temperature in the bodies. If we touch 

 the bodies, the state of their temperature, which means the rate of 

 their molecular vibration, sends an agitation to the brain which is there 

 arrested by a new friction and given the new form called heat. Thus 

 we have friction representing arrested energy with a rise of temperature 

 of so many degrees as its measure, in the environment; and we have 

 friction of arrested energy in the brain measured by a quantity of heat. 

 Thus the heat is sensation and its seat is in the brain and not in the ex- 

 ternal object of high temperature. I know I am insisting here on what 

 everybody knows, but I am sure but few realize that heat is a motion of 



