LOCALfSATlON OV (JKO-PERCEPTIVE LAYER VX\ 



two sides might result from the passive yielding to the 

 definite reaction iiuiuced on tiie opposite side. Investiga- 

 tion l)y the electric method enables us, however, to dis- 

 criminate the two reactions from each other, since the 

 electric response characteristic of the induced physiological 

 change takes place in the organ, even under condition of 

 restraint by which movement is prevented. We shall there- 

 fore investigate the geo-electrical. reaction on the lower side 

 of the securely held organ, and find out whether the 

 induced electric change undergoes any variation in different 

 layers from below upwards. There are two different ways 

 in which the electric explorations of the lower side of the 

 organ may be carried out. In the first method, the probe 

 is introduced from below, and saecessive readings for geo- 

 electric response taken as the probe enters the organ by 

 successive steps. It is understood that the true geotropic 

 effect is found from difference of galvanometer readings 

 in vertical and horizontal positions. In the second 

 method, the probe is intro<luced from above, and successive 

 readings for the response taken for different positions of 

 the probe as it enters the organ from the upper side and 

 comes out ultimately at the lower side. This I shall call 

 the METHOD OF TRANSVERSE PERFORATION. The intru- 

 sion of the probe on the upper side gives, as we have seen, 

 increasing negative deflection of the galvanometer which 

 reaches a maximum at the perceptive layer. Passage of the 

 probe to still greater depths give deflections which decline 

 to zero. But when the probe comes within the influence 

 of the perceptive layer of the under side, the electric 

 indication, as we shall presently find, undergoes a reversal. 



ELECTRIC EXPLORATION OP THE LOWER SIDE OF THE 



ORGAN. 



I shall first describe the results oV»tained fi-om tlu- first 

 method, the prolx' entering the organ from the lowtM- side. 



