RESPONSE OF EPITHELIUM AND GLANDS 327 



The secondary was next brought back to its original position 

 and a record once more taken of its successive responses 

 to stimuli of the same intensity as before. It will be seen 

 (fig. 197, b) that the response is completely reversed by the 

 relative depression of the excitability of the lower surface 

 B. Similar reversal under fatigue will be shown in the 

 glandular organ of Drosera in the next chapter (fig. 208). 

 I have obtained other interesting variations of normal 

 response induced by fatigue. Thus, taking the carpel of 

 Dillenia indica, and making electrical contacts with its inner 

 and outer surfaces, the responses under moderate stimulus 

 were found to be normal that is to say, from inner to outer 

 the secondary being here understood to be partially over- 

 lapping the primary at a distance of six divisions of the 

 scale. The secondary was now pushed home, and the tissue 

 subjected for a short time to strong and continuous stimula- 

 tion. Moderate fatigue was thus induced. When the 

 secondary was now brought back to the distance of six 

 divisions of the scale the response was found to be reversed. 

 Thus, moderate fatigue had here been sufficient to bring 



(about the reversal of -the relative excitabilities of the two 

 surfaces of the carpel of Dillenia indica, when the testing 

 stimulus was of original intensity. But when the intensity 

 of stimulus was increased, by pushing in the secondary to a 

 position marked three divisions on the scale, the response 

 became once more normal. Thus, fatigue had in this case 

 modified the excitability of the two surfaces in such a way 

 that an intensity of stimulus, which was formerly effective to 

 induce greater excitation of the originally more excitable, was 

 now ineffective ; and its greater excitation, with the restoration 

 of normal response, could now only be evoked under stronger 

 stimulus. 



We shall next describe the reversal ot normal response 

 under sub-minimal stimulation. For this we shall once 

 more select the carpel of Dillenia indica. A record of its 

 normal response the direction being from inner to outer is 

 given in the first series of records in fig. 199. After taking 



