RESPONSE OF DIGESTIVE ORGANS. 339 



trends upwards. This indicates that the glandular surface, 

 by the residual effect of stimulation, is being rendered more 

 and more galvanometrically negative. This explains why 

 the internal surface of the stomach has been found by 

 different observers to be negative, a condition of more or 

 less persistent negativity being thus clearly due to the ex- 

 citatory after-effect of preparation. Had it not been for the 

 exceptional opportunity afforded by the open pitcher of 

 Nepenthe, it would have been impossible to make galvano- 

 metric connections with the intact inner glandular surface 

 and thus to ascertain that such a surface is naturally gal- 

 vanometrically positive. 



I may here point out the very interesting modifica- 

 tion of response which occurs in the same specimen under 

 a long-continued series of stimulations. This modification, 

 due to fatigue so-called, makes its appearance first in dimi- 

 nution of the height of the responses. Some of the con- 

 stituent multiple responses due to a single stimulus are 

 then found to be reversed to positive, and after this they 

 show a tendency to become more or less completely 

 reversed. 



It is also interesting to find that the same modifications 

 make their appearance, in the same order, in those pitchers 

 which have been subjected to continuous stimulation, to a 

 greater or less extent, by the supply of insects. That is 

 to say, a pitcher containing a few insects is found to give 

 responses, the multiple constituents of which are sometimes 

 positive and sometimes negative. This intermediate phase is 

 seen well illustrated in the record given in fig. 204. But in 

 the pitcher whose inner surface is already thickly coated with 

 insects, and which has long been exposed to the continuous 

 action of such stimulation, the characteristic response is 

 found to be the reverse of that of the fresh specimen. It 

 will be seen from the record in fig. 205 that in such a case 

 the individual effect of a single stimulus is a series of mul- 

 tiple responses which are positive. In this record a curious 

 effect is again seen, that of the shifting of the base-line, now 



z 2 



