264 APPENDIX. [No. XVII. 



may be termed CcBnaisthenics. We are also enabled to judge of the 

 changes taking place within our own body, which estimation may be 

 more properly called Somaisthenics. By Somaisthenics we are enabled 

 to estimate the slightest muscular motion, and, in fact, I cannot move 

 my finger or my arm to even the slightest extent without having a 

 perfectly distinct idea of the amount of motion produced. 



The skin is acted upon by variations of temperature and force : 

 hence we have to inquire how far heat and force can be employed to 

 set in motion the voltaic force. In experimenting upon the variations 

 of temperature, I found a large series of thermo-voltaic circuits, which, 

 curiously enough, are analogical to photo-voltaic circxdts, inasmuch as 

 heat, at various times, determines both negative and positive circuits in the 

 same manner as Kght. I have here a negative thermo-voltaic circuit. The 

 apparatus, as you perceive, consists of a V-tube, containing sulphate of 

 copper. Into each side of the tube a copper wire is placed, and you 

 perceive that the moment I apply the heat of a spirit-lamp to one side 

 the galvanometer is very strongly deflected, the heated side becoming the 

 negative pole. 



When force acts upon the skin, I presume the blood-corpuscle is pre- 

 vented from coming in contact with the termination of the nerve-fibre ; 

 and I wiU beg you to bear this supposition in mind, as in a later part of 

 this lecture I shall demonstrate to you, that if this supposition be correct, 

 a voltaic circuit must be generated. My observations upon heat and 

 force simply indicate that a thermo- or dynamo-voltaic circuit is an 

 ordinary voltaic or physical phenomenon; but that by no means proves 

 that in the living body the mechanism of feeling is voltaic. This, however, 

 is an experiment easily shown, for we have but to introduce our electro- 

 voltaic test into the cutaneous textures, when a powerful deflection of the 

 galvanometer occurs whenever we pinch or otherwise irritate the skin. We 

 thus find that the mechanism of all the sensations is voltaic, and, according 

 to the laws of the voltaic test, the needle nearest the negative pole becomes 

 positive ; that nearest the positive pole, negative. From direct expeiiment 

 I should therefore infer, that the organs of sensation all constitute the 

 positive pole of the peripheral battery. These inferences, however, must 

 always be taken with a proper allowance for the complex character of the 

 voltaic circuits in the body, or rather, I would say, for the complex 

 materials of which the circuit is composed. 



Sensations are received by a certain definite number of sensor nerves, 

 which constitute the only means we possess of obtaining a knowledge of 

 the external world. The sensor nerves pass to the brain, and then come 

 in contact with a highly vascular tissue, called the grey matter of the 

 brain ; and I invite your attention to the very exquisite injections which 

 I have made of that tissue, by means of the solution of cannine, and 

 which will be exhibited under the microscope in the library after the 

 lecture. 



Inasmuch as the sensor nerves come in contact with blood-vessels, it 

 follows from voltaic laws, that a voltaic battery exists in the brain, which 

 is opposed to that in the body, and by which the electro-biological circuit 

 is completed. At this point we leave the regions of direct experiment, 

 and we must deduce the mechanism of the central battery according to 

 voltaic laws on the one hand, and the properties of the mind on the other. 



