Abstract

The following summary expresses the results of a study of the action of physostigmine and of atropine on strips from different type regions of the heart of the turtle, species Chrysemys belli and C. marginata.

1. Physostigmine applied to automatically rhythmic strips from the sinus and from the auricular apex made rhythmic by barium chloride produces slowing and complete stopping of the normal fundamental rhythm.

2. Physostigmine does not stop the contractions of ventricular muscle automatic in saline-Ringer mixtures, which is evidence against the presence of parasympathetic nerves to the ventricle.

3. Physostigmine does not influence the tone contractions of the sinus muscle or of the auricular apex. This is most conclusively shown in auricular apex strips producing full tone contractions but no fundamental contractions.

4. Atropine completely antagonizes the inhibition of the fundamental rhythm produced by physostigmine.

5. Atropine has no characteristic effect on the tone contractions of cardiac strips of either the sinus or the auricle.

6. After atropine, previously tested active concentrations of physostigmine have no further effect on cardiac rhythm.

7. Physostigmine does not affect cardiac muscle by direct action. This is true for all regions of the heart.

8. The ventricular apex strip is free of all tone contractions. Hence, it is judged to be free from smooth muscle.