Fig. 37.—The Glass Chamber containing the Plant
Amplitude of vibration which determines the intensity of stimulus is measured by the graduated circle seen to the right. Temperature is regulated by the electric heating coil R. For experiments on action of anæsthetics, vapour of chloroform is blown in through the side tube.
Electric heating.—The experiments just described were, however, rather troublesome, inasmuch as, in order to produce each variation of temperature, the specimen had to be taken out of the apparatus, warmed, and remounted. I therefore introduced a modification by which this difficulty was obviated. The specimen was now enclosed in a glass chamber ([fig. 37]), which also contained a spiral of German-silver wire, through which electric currents could be sent, for the purpose of heating the chamber. By varying the intensity of the current, the temperature could be regulated at will. The specimen chosen for experiment was the leaf-stalk of celery. It was kept at each given temperature for ten minutes, and two records were taken during that time. It was then raised by 10° C., and the same process was repeated. It will be noticed from the record ([fig. 38]) that in this particular case, as the temperature rose from 20° C. to 30° C., there was a marked diminution of response. At the same time, in this case at least, recovery was quicker. At 20° C., for example, the response was 21 dns., and the recovery was not complete in the course of a minute. At 30° C., however, the response had been reduced to 7·5 divisions, but there was almost complete recovery in twelve seconds. As the temperature was gradually increased, a continuous decrease of response occurred. This diminution of response with increased temperature appears to be universal, but the quickening of recovery may be true of individual cases only.
Fig. 38.—Effect of Temperature on Response
The response was abolished at the hot-water temperature of 55° C.
Table showing Diminution of Response with Increasing Temperature
(·01 Volt = 35 divisions)
| Temperature | Response |
|---|---|
| 20° | 21 |
| 30° | 7·5 |
| 40° | 5·5 |
| 50° | 4 |
| 65° | 3 |