464 REPORTS ON THE STATE OF SCIENCE. 



addressed ourselves was whether the sudden application of heat — a thermic 

 shock, so to speak — could act as a true stimulus in the sense that an 

 electric shock acts as a stimulus. Our results in this connection are 

 not yet published ; I may, however, so far anticipate them by stating — 



(1) That as regards animal nerves the experimental answer is clearly 

 negative. 



(2) That as regards vegetable tissues the answer is in all probability 

 negative, the effects of thermic shocks being, in my opinion, due to move- 

 ments of water rather than to excited and transmitted protoplasmic 

 activity. 



(3) That the above two considerations lead to the reinvestigation of 

 Hermann's fundamental principle to the effect that warmer tissue is 

 galvanometrically positive to cooler tissue.' 



This third point will, I hope, form the subject-matter of an early 

 communication to the Physiological Society. At present I am not 

 sure of the fact as stated by Hermann, nor therefore obviously of its 

 possible interpretation, as to whether it be due to unequal ionic velocities 

 of dissociating molecules or to mere water movements from or towards 

 the heated spot. 



The problem of transmission in vegetable protoplasm in the definite 

 restricted sense of the propagation of an excited state from cell to cell 

 has been previously approached by several observers and theorists. 



The principal authors to whom I have referred have been Burdon 

 Sanderson, Haberlandt, Nemec, and Bose. 



My first definite knowledge - of the question of transmission of the 

 pxcitatory state in plant protoplasm was denied from the papers of 

 Burdon Sanderson on Dioncea. In the course of the observations by 

 which he sought to establish a comparison between vegetable and animal 

 tissues as regards their meclianical and electrical responses to excitation, 

 he showed that, in consequence of mechanical or electrical excitation of 

 a hairlet, an electrical response of an opposite lobe of the leaf of Dioncea 

 took place, thus clearly proving that in the case of a sensitive plant 

 transmission of excitation does actually occur. In fig. 10, p. 21,-* a 

 diagram of what he terms tlie fundamental experiment is given in whicli 

 ail electrical response of one lobe is observed consequent upon an electrical 

 excitation applied to the other lobe. With some reservation (p. 40) he 

 gives as the probable rate of transmission ' at least 200 mm. per second.' 

 In his second paper ^ Burdon Sanderson (pp. 444, 445) gives the rate as 

 200 to 300 mm. per second, according to temperature, and explicitly 

 concludes that ' the excitatory process in the leaf is of the same nature 

 as that which follows stimulation in animal structures, and more 

 particularly in nerve.' And the beautiful electrometer records given 

 in illustration of this paper exhibit diphasic effects in Dioncea essentially 



' Pniiger's ArnJiiv, vol. iv. 1871, p. 1G3. 



- Tlirough the writings of Claude Bernard, and bis description of the action of 

 anesthetics on Mimosa, my attention Lad been dii-ected to the previous observations 

 of Dutrochet (182i), who first measured the speed of propagation in Mimosa, and 

 gave it as being 2 to 3 mm. per second. Paul iJert (1870) gave it as being 

 2 to 5 mm. per second. 



" Phil. Trans., ISSl, 'On the Electromotive Properties of the Leaf of Dioncea 

 la the excited and unexcited states.' 



« lUd., 1888. 



