Fig. 37.—Antagonistic action of alkali and acid. Arrest of response in contraction under NaOH (↑), restoration and final arrest in expansion under lactic acid. (↑)
Antagonistic actions of Alkali and Acid: Experiment 29.—Alkali and acid are known to exert antagonistic actions on the spontaneous beat of the heart; dilute solution of NaOH arrests the beat of the heart in systolic contraction, while dilute lactic acid arrests the beat in diastolic expansion. I have found identical antagonistic reactions in the pulsating tissue of Desmodium gyrans, the telegraph plant. It is very interesting to find that these agents also exert their characteristic effects on the response of Mimosa in a manner which is precisely the same. This is seen illustrated in Fig. 37, where the application of NaOH arrested the response in a contracted state; after this, the antagonistic effect of dilute lactic acid is seen first, in its power of restoring the excitability; its continued application, however, causes a second arrest, but this time in a state of relaxed expansion.
CuSO4 Solution.—This agent acts as a poison, causing a gradual diminution of amplitude of response, culminating in actual arrest at death. Certain poisons, again, exhibit another striking symptom at the moment of death, an account of which will be given in a separate paper.
EFFECT OF “FATIGUE” ON RESPONSE.
Fig. 38.—“Fatigue” induced by shortening intervening period of rest.
With Mimosa, after each excitation the recovery becomes complete after a resting period of about 15 min. With this interval of rest the successive responses for a given stimulus are equal, and are at their maximum.