202 



COMPARATIVE ELECTRO-PHYSIOLOGY 



point of instability, already noticed in the thermo- mechanical 

 curve, was often found to occur at or about 55 C. And 

 if the specimen were not in favourable tonic condition, or 

 had been suffering from injury, the death-point was lowered 

 to this degree. 



I give below an electrical curve showing the point of 

 inversion at death (fig. 132). It was obtained with the 



sheathing petiole of Musa. The 

 inner or concave side of this petiole 

 is more excitable, as we have seen, 

 than the outer. These responsive 

 electrical variations were very large, 

 and could not be represented within 

 the limits of the photographic plate. 

 I therefore took a photographic 

 record between the temperature of 

 54 C. and 67 C. only. The first 

 part of the curve represents the 

 increasing galvanometric posi- 

 tivity of the more excitable inner 

 surface of the specimen. The 

 same process of increasing posi- 

 tivity under the continuous rise of 

 temperature, had been going on 

 previously, it is to be understood, 

 before arrival at 54 C., at which 

 the photographic record was com- 

 menced. This increasing galvano- 

 metric positivity corresponds to 

 the gradual erection of the leaf in 

 Mimosa, and to the expansion of 

 a radial organ, such as a coronal 

 filament of Passiflora, all alike being due to the positive 

 variation of turgidity. In order to give an indication of the 

 particular temperature at each portion of the curve, the re- 

 cording light was obscured for about 1 5 seconds after each 

 degree of temperature. The successive gaps, then, are one 



FIG. 132. Photographic Record 

 exhibiting Electric Spasm in 

 the Petiole of Musa 



Sudden electric inversion takes 

 place at the death-point, 

 59*5. Record was com- 

 menced at 54 C., and suc- 

 cessive gaps in the record 

 indicate i C. rise of tem- 

 perature. 



