This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
So-called cardiac poisons. With a larger dose the stage of stimulation is followed by, one of peristaltic action, and final arrest in systole.1
Caffeine (produces rigor).
In small doses.
[Depression is shown by diminished energy of contraction with final stoppage in diastole. The cardiac muscle is shown to be paralysed by no longer contracting on stimulation, either mechanical or electrical.]
Salicylic acid. Potassium salts. Copper double salts. Zinc double salts.
In large doses.
Saponin (removes the systolic still-stand produced by digitalin).
Veratrum viride (veratroidine and jervine).
These do not" cause peristalsis, nor arrest in systole. They excite the heart to pulsate rhythmically, after it has been made to stand completely still in diastole by the application of muscarine.
[Stimulation is shown by increased rapidity and energy of contraction, which is observed, not only when the drug is given to an animal, but when it is applied directly to the heart.]
[Depression is evidenced by slower and less powerful pulsations, with final stoppage in diastole. This stoppage is shown to be due to the action of the drug on the ganglia, and not on the cardiac muscle, by the heart contracting on stimulation, either mechanical or electrical, after spontaneous pulsation has ceased.]
Antimony (?). The stoppage in diastole caused by antimony is converted into stoppage in systole by helleborein. Hydrocyanic acid. The same drugs that stimulate in small doses depress when used in larger quantity, or at a later stage of their action.
1 This stoppage of the heart in systole occurs in frogs, but in higher animals the heart may stop in diastole.