THE EFFECT OF PHYSOSTIGMINE ON THE RESPONSES OF EARTHWORM BODY WALL PREPARATIONS TO SUCCESSIVE STIMULI

¹ From the Department of Zoölogy, Connecticut College, and the Marine Biological Laboratory, Woods Hole, Mass.

1. The longitudinal muscles of the body wall of the earthworm (Lumbricus terrestris) show augmented responses when stimulated by successive single shocks at low frequencies. The facilitating condition lasts not more than 0.5 second after the response to a single shock.

2. A frequency of 14 per second results in a complete summation of the contractions or a condition of tetanus.

3. The magnitude of a summated response elicited by a series of shocks is proportional to the duration of the burst of shocks and to the frequency of the shocks within the burst.

4. The tetanic responses to repeated bursts of stimuli show an increasing augmentation of the initial contractions. The production of this "staircase" effect is affected by the frequency of the shocks, the duration of the bursts, and the length of the interval between bursts.

5. After a brief tetanus the facilitating condition persists for nearly 30 seconds.

6. The application of physostigmine increases the augmentation of responses and tends to produce a condition of tonus.

7. Physostigmine delays the decay of the facilitating property so that augmented responses are produced with intervals as long as 3 minutes between bursts of stimuli, suggesting the rôle of acetylcholine in the production of the augmented responses.