82 THE SIGNS OF LIFE [LECT. 



a good deal of trouble if you wanted to control statements 

 concerning the Torpedo. 



49. Its direction. The direction of response to stimuli of 

 both directions is an indication of the natural direction of 

 organ response. The strip of organ discharges in the way 

 determined by its structural and functional disposition. Can we 

 trace any analogous disposition in the case of the analagous 

 response of eye or skin ? May we consider that the direction of 

 a blaze-current is in any measure determined by structural and 

 functional disposition of organ ; or, otherwise expressed, have we 

 any right to attribute an organ-current to such structures ? I 

 think there are reasons for and reasons against an affirmative 

 answer. As regards the eye, we have positive response to light 

 and positive response to both directions of electrical excitation. 

 We also have negative response to light and negative response 

 to both directions of electrical excitation. But here is no 

 definite and fixed direction of organ-discharge, only a pre- 

 dominance, fluctuating with state of organ and kind of animal. 



50. The skin-discharge. As regards the skin, we have 

 positive response and negative response to indirect excitation, 

 and almost exclusively positive (outgoing) response to direct 

 electrical excitation of whatever direction. Here, again, is no 

 definite and fixed direction of organ-discharge by the natural 

 mode of action through nervous channels, but a marked pre- 

 dominance in one (the outgoing) direction in response to both 

 directions of electrical excitation. 



With direct excitation of the skin, we must suppose that all 

 its living parts are aroused to action, gland cells and general 

 epithelium alike, and we may not attribute the effect to any one 

 kind of tissue element to the exclusion of others. We know by 

 experiment, however, that the action proceeds from elements 

 at or near the external surface ; and we find further that with 

 shavings of skin, including Malphigian layer and excluding the 

 deeper situated glands, the direct response is obtained as before, 

 while with shavings of cuticle only, no response whatever is 

 obtained. Mercuric chloride, which, as you saw, abolished the 



