374 Dr. J. Bur don-Sanderson and F. J. M. Page. [May 13,. 



exist as soon as its effect is over; (2) by diminished excitability 

 (showing itself in the suspension or diminution of the power which 

 the structure before possessed of responding to a second excita- 

 tion) ; (3) by the fact that it is propagated from the part first excited 

 to contiguous parts at a rate which is different in different structures, 

 and in the same structure at different temperatures. Hitherto the 

 relations of these three facts have been chiefly studied in the excitable 

 tissues of the higher animals. Our investigations lead us to conclude 

 that they are equally characteristic of the excitatory state in plants. 

 We attach great importance to them, as being the only outward and 

 visible signs by which the hidden process of excitation constantly 

 reveals itself. For those more obvious changes which, in the con- 

 tractile structures, follow excitation, are wanting in those which are 

 merely excitable, and thereby lose their value as characteristics. 



It was from the first apparent that the physiological relations of the 

 three kinds of phenomena which admitted of investigation, viz., those- 

 of electrical change, of diminished excitability, and of propagation, 

 could only be learnt by the use of exact methods for the determination 

 of the order of occurrence and duration, i.e., of the time-relations of 

 each. For this purpose the means were then wanting ; the first step 

 was to contrive and construct the instrument, of which the description 

 has just been given. The rheotome was completed in April, 1879, 

 since which time the observations now communicated have been made. 



Shortly after the communication of our last experiments, Pro- 

 fessor Engelmann made a valuable addition to the researches* 

 previously published by him on the electrical phenomena of the 

 excitatory process in the ventricle of the heart of the frog. The 

 most important of his results and conclusions are as follows : — 

 (1) In 47 out of 78 preparations, investigated with the aid of 

 Bernstein's rheotome, it was found that, when the surface of the 

 separated ventricle ("ventricle- apex preparation") was excited by the 

 passage of a single induction shock between platinum electrodes in 

 contact with its surface and not more than a millimeter apart, the- 

 surface being led off, as in our experiments, by two contacts at 

 unequal distances from the seat of excitation, the nearest of the two 

 led-off surfaces (2 millims. distant), became first negative, then 

 positive to the other (5 millims. distant). Thus the variation assumed 

 the character of a " Doppelschwcmhung" i.e., it consisted of two 

 phases of opposite signs. In the remaining 31 instances, all that was 

 observed was that the nearer contact became at once negative, and that 

 its negativity gradually subsided. (2) In' 33 experiments in which the 

 same method was employed, the means of the deflections of the 

 galvanometer, corresponding to the first four-tenths of a second after 



* " Ueber das electrische Yerhalten des tliatigen Herzens," " Pfhiger's Arcliiv," 

 -vol. xvii, p. 68. 



