REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 705 



while the current of rest flows from the exposed upper to 

 the protected lower surface, the direction of the responsive 

 current is opposite, namely from the lower to the upper, 

 proving that the protected lower is the more excitable of 

 the two. Similarly, in the case of the intact human lip, I 

 found that the resting current was from the epidermal to 

 the epithelial, the responsive current being in the opposite 

 direction (fig. 196). Again, on testing the differential 

 response of armpit and shoulder, I found that the respon- 

 sive current was from armpit to shoulder, the former being 

 thus the more excitable of the two (fig. 194). 



We have seen that the lining membrane of the inner 

 surface of the peduncle of Uriclis lily is very thin, and that, 

 in distinction to the outer or epidermal membrane, it may be 

 regarded as epithelial. As we approach the bulb-end of the 

 peduncle, this inner layer of cells is found to be highly turgid, 

 and secretion is found to take place into the hollow tube. 

 The inner surface of the carpellary leaf of Dillenia indica, 

 again, secretes a mucilaginous substance. In these two cases 

 there are no definite glands. But definite glands are found to 

 occur on the inside of the pitcher of Nepenthe. In all these 

 cases the secreting layer, whether provided with glands or 

 not, is found to be very highly excitable, and to respond 

 by strong galvanometric negativity. Taking a carpel of 

 Dillenia indica, it is found that the natural current is from 

 the outer epidermal to the inner secreting surface, the respon- 

 sive current being in the opposite direction. On making very 

 careful connections, with the skin of the protruded body of 

 the snail, and the glandular under-surface of its foot, it is 

 found that the natural current is from the non-glandular to 

 the glandular, but the responsive current from glandular to 

 non-glandular. As an example of the way in which the 

 true natural current of rest may be reversed by the excitatory 

 effect of preparation, I showed that, while in the intact snail 

 the natural current was from non-glandular to glandular 

 the gland being in this case relatively positive, to the extent 

 of -0013 volt after the sectioning of the foot, the original 



z z 



