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.
Irritants of motor centres.
[Little or nothing is known about the depression of the accelerating centres.
Saponin paralyses accelerating nerves.
[Stimulation is shown by a rise in blood-pressure which remains after section of the spinal cord at the occiput, and is produced by the injection of the drug after previous division of the cord. It is also ascertained by the rate of flow through the vessels being diminished by the drug when circulation is kept up artificially in a frog whose nerve-centres have been destroyed, or in a single limb of a warm-blooded animal.]
Digitalis and its allies.
[Depression is shown by a fall of blood-pressure to a slight extent, even after the spinal cord has been divided, and by increased rapidity of flow when artificial circulation is kept up.]
[It is very doubtful whether they are stimulated by drugs, and at any rate it is very difficult to ascertain whether any stimulation which may occur in the arterioles or capillaries is in the terminations of the vaso-motor nerves or in the muscular walls.]
[Paralysis is shown by the vessels not contracting on stimulation of the vasomotor nerves, while they still contract on direct stimulation. This has been chiefly observed in the vessels of the intestines after irritation of the splanchnic nerves. The effect of irritation is ascertained by the alterations in colour of the intestines, and also by the alterations in the general blood-pressure which occur after irritation.]