Page:Collected Physical Papers.djvu/330

310

A block is produced by clamping the plant in the middle at C; increased stimulation is found to occur in the tissue by increased amplitude of vibration.

l now proceed to demonstrate that the response given by the plant is physiological and that it affords an accurate index of the vital activity of the plant. For it will be found that whatever tends to exalt or depress this activity also tends to increase or diminish the intensity of electric response.

The test applied by physiologists, in order to discriminate as to the physiological nature of the response consists in observing the effects of anæsthetics, poisons, and exceedingly high temperatures, all of which are known to depress or destroy the activity of life.

Effect of Anæsthetics and Poisons.—I took 30 leaf-stalks of horse-chestnut, and divided them into 3 batches, of 10 each. One batch was kept in water, to serve as control experiment, another in chloroform water, and the third in a 5 per cent. solution of mercuric chloride.

Average response of stalks kept in water = 23 divisions.

Average response of stalks kept in chloroform = 1 division.

The response of stalks kept in poisonous mercuric chloride was completely abolished.

Effect of High Temperature.—A leaf-stalk is taken, and using the block method strong responses are obtained at both ends A and B. The stalk is now immersed for a short time in water at 60° C. After this treatment