n8 



COMPARATIVE ELECTRO-PHYSIOLOGY 



the natural current. Diminution of internal energy on the 

 other hand might be expected to cause a negative variation, 

 These effects are diagrammatically represented in fig. 83, 

 which also exhibits the parallelism between the electric 

 responses of motile pulvinus and non-motile anisotropic 

 organ. 



We next proceed to subject the question of the effect of 

 increased or diminished internal energy on the natural 

 current to experimental verification. As regards the increase 

 of internal energy, we have already seen that this can 



be secured by a gradually 

 rising temperature, its 

 diminution being, con- 

 trariwise, secured by a 

 falling temperature. In 

 the case of Mimosa, we 

 saw that the former in- 

 duced an erection of the 



Upper and less excitable surface of former l eaves , and the latter a 

 corresponds with outer or convex sur- 

 face of latter. The natural current, N, 

 is in both from the less to the more ex- 

 citable. In both excitatory current, E, 

 is in opposite direction, i.e. from the 

 more to the less excitable. In Miisa 

 increase of internal energy ( + | ) in- 

 duces a positivej and diminution of 

 internal energy ( - * ) a negative, varia- 



FlG. 83. Parallelism of Natural Current 

 in Pulvinus of Mimosa and Sheathing 

 Petiole of Musa 



tion of the natural current. 



gradual depression. In 

 order, then, to observe the 

 effect of increase or de- 

 crease of internal energy 

 on the existing current of 

 rest, we have only to sub- 

 ject the specimen to gradual 

 and record the consequent 



thermal ascent or descent, 

 variation of current. 



The specimen of Musa is placed in a chamber and two 

 diametrically opposite contacts are made, with the internal 

 and external surfaces, and led off to the galvanometer. To 

 take first the effect of cooling : a stream of ice-cold water is 

 sent through a hollow tube in the chamber : this gradually 

 lowers the temperature, say from 30 C. to 27 C. It will be 

 seen from left-hand curve of fig. 84 that this has the effect 

 of diminishing the natural current of rest in the tissue, as 

 represented by the dotted arrow j. When the chamber is 



