284 



COMPARATIVE ELECTRO-PHYSIOLOGY 



thermal stimulation, to flow from the more excitable concave 

 to the less excitable convex. In order next to demonstrate 

 the physiological character of these responses, I subjected 

 the tissue to the action of chloroform, and the record in the 

 second part of the figure shows the consequent depression 

 of the response. 



The great delicacy and pliability of this mode of applica- 

 tion of stimulus enable us to attack many difficult problems, 



on the difference of excit- 

 ability between two points in 

 a tissue, with perfect ease. 

 To -how many distinct in- 

 vestigations it can be suc- 

 cessfully applied will be set 

 forth in detail in succeeding 

 chapters. As there is nothing 

 to prevent the two exploring 

 electrodes from being applied 

 on any two points, however 

 distant, of the same organism, 

 it is seen that we have here 

 a means of determining, not 

 only the differential excit- 

 ability of any two points of 

 the same organ, but also that of any two organs of the same 

 specimen. For the present I shall, however, content myself 

 with giving a few instances only in illustration of the ex- 

 treme delicacy of this method in detecting physiological 

 differences as between two points. 



We shall first turn our attention to those physiological 

 modifications which are due to the a-symmetrical action of 

 the environment on the organism, and here we shall select 

 the case of the plagiotropic stem of Cucurbita. We have 

 seen that in the recumbent stem of this plant the tissue of 

 the upper side is rendered relatively fatigued by the con- 

 tinuous action of sunlight, and thus becomes permanently 

 less excitable than the lower side. We have also found that 



FIG. 173. Photographic Record of Re- 

 sponse of Petiole of Mtisa to Equi- 

 alternating Electric Shocks, before 

 and after Application of Chloroform. 



