1882.] on Aniynal Excitability. 147 



morning in that year, that if such were found to be the case it would 

 afford strong confirmation of the view to which he had been led by 

 entirely different considerations, of the close eolation which subsists 

 between the essential vital processes of plants and animals, I under- 

 took at once to examine into the subject. It was the rough result of 

 that inquir}^ that I brought before you in lh74. What we expected 

 to observe was observed. It was found that in the leaf of Dioncea 

 miiscipula, which was selected as the example of plant-excitability 

 best adapted for the purpose, the touching of the sensitive hairs was 

 immediately followed by an electrical disturbance, w^hich preceded 

 the visible motion of the leaf. As the electrical phenomena observed 

 strikingly resembled those which present themselves under similar 

 conditions in animals, there seemed no room for doubt that the analogy 

 which had suggested the discovery was a true one. But in 1876, 

 Professor Muuk, of Berlin, an animal physiologist of the highest 

 reputation, published an elaborate paper on Dionaea, in which, while 

 he admitted that the facts which had been recorded were in the main 

 true, and that a real relation existed between the electrical disturbance 

 which follows excitation in Dionaea and the so-called *' negative 

 variation " of animal physiology, he charged me with having entirely 

 misinterpreted and misunderstood that relation ; and in 1877 another 

 still more important research was j)ublished by Dr. Kunkel, in which 

 the question was approached from the side of plant-physiology. 

 Professor Kunkel's experiments related not to Dionaaa but to Mimosa. 

 His conclusions were as directly opposed to those of Dr. Munk as 

 they were to mine ; for his main position was that all electromotive 

 phenomena observed in the organs of j)lants, are dependent on changes 

 in the distribution of water in their tissues, and consequently have 

 nothing whatever in common with the electromotive phenomena of 

 muscle and nerve. Even had there not been other good reasons for 

 resuming the investigation of the subject, this contradiction of opinion 

 would have rendered it necessary. 



Every one who contemplates the behaviour of the sensitive plant, 

 or of the Flytrap, is led to exclaim : If it had but nerves we could 

 understand it ! Let us for a moment inquire what there is in nerve 

 which these animal-plants seem to require. The question is easily 

 answered. Nerve is the channel by which, in the animal body, the 

 influence of any change which takes place in one part of the organism 

 is conveyed to other parts at a distance, indej)endently of the trans- 

 mission of any sensible motion. Haller, who is well called the 

 father of physiology, sought to explain the propagation of influence 

 in nerve, from the organ of the will to the muscles which it governs, 

 by the transmission of motion of liquid contained in a tube (as in 

 this little apparatus in which my hand represents the will, the long 

 flexible tube the nerve, and the indicator at its farther end the 

 muscle). It is more than a century since Haller made this com- 

 parison, but even then he was behind his time, for a greater than he 

 — Newton — had clearly recognised that the process by which the 



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