THE ACTIVE FORCES OF LIVING ORGANISMS 49 



we have conclusive evidence, we may certainly infer 

 either chemical or molecular action. Has, indeed, we 

 may ask, an electrical current ever been known to 

 exist which has not originated in, been accompanied 

 by, or given rise to, chemical — that is to say, atomic — 

 action or to molecular vibration ? When the lightning 

 flashes from the clouds on a midsummer's day, are 

 not the molecules of water and air vibrating intensely, 

 owing to the heat and friction to which they are sub- 

 jected ? When a very powerful current of electricity 

 is made to pass along a thin copper wire, will it not 

 cause the molecules to vibrate until they glow with 

 red-hot intensity ? May we not believe, therefore, Tiie three' 



•' ■' . . . elements. 



that the presence of electrical action in a nerve fibre 

 indicates that molecular vibration is taking place ? 

 The molecular element seems the more essential, 

 since without it it would be very difficult to explain 

 all the varieties of sensation, especially those forms 

 of it in which no end organ participates and, as far 

 as the periphery is concerned, little or no chemical 

 action is observable. In this category must be 

 classed many effects due to the tactile sense and 

 others belonging to the muscular sense. Some effects, 

 again, such as the lighter ones of the tactile kind, as, 

 for instance, tickling with a hair, seem so insignifi- 

 cant as almost to suggest an electrical origin, or, at 

 least, that electrical variation plays an important 

 part in them. In all such cases, if we exclude the 

 latter, molecular transmission is the only explanation 

 on which we can fall back ; and it seems justifiable, 



4 



