CONDUCTIVITY AND EXCITABILITY 22 5 



without directly affects the outer layer of the tissue, and the 

 excitation may then proceed inwards and in lateral directions, 

 by conduction. 



The effect of ether in diminishing receptive excitability 

 may be demonstrated by taking, as in the last case, a specimen 

 of Biophytum, We first test the specimen by applying a 

 moderate stimulus on the stem at E. The excitation thus 

 initiated at the receptive area is transmitted to the leaves, 

 and causes depression of their leaflets. When these have 

 recovered, ether is applied locally on the area E. On now 

 repeating the stimulation, we find that none of the leaflets 

 respond. Since the conductivity of the intervening tissue 

 and the excitability of the motile organs have remained 

 unaffected, it is clear that the failure to respond is in this 

 case due to the depression of receptive excitability by ether. 



A tissue, however, whose superficial excitability is depressed 

 in this way, may still retain the power of conduction. This is 

 shown by applying stimulus on the stem, as in the last ex- 

 periment, but at x , below the etherised ring E. The stimulus 

 is now shown to be transmitted, by the fall of the motile 

 leaflets. The explanation of this difference probably lies in 

 the fact that the molecular torpidity induced by the etherisa- 

 tion does not extend very deep, unless it has been excessive 

 and long-continued. In that case, the internal layer of the 

 tissue, remaining unaffected, would serve as the channel of 

 conduction. This view is supported by the fact which I 

 have noticed, that it is much easier to produce a complete 

 block to the passage of stimulation, when a relatively thin 

 tissue, such as the petiole of a leaf, is etherised. It is much 

 more difficult, on the other hand, to do this with a thick 

 stem. 



We saw from the molecular model (fig. 94) that though 

 when the molecules were sluggish no response could be 

 obtained to moderate stimulus, yet when the stimulus was 

 very strong response could be brought about. Similarly, in 

 experimenting on plants, I have found it possible, by careful 

 graduation of etherisation, to arrange matters in such a way 



