When a muscle is irritated at one point, the contraction wave which occurs at that point is conducted along the muscle in both directions.

This contraction wave, like that which occurs in the contractile tissue of the medusa, is independent of the nervous system. The completeness with which it is conducted, and the quickness with which it subsides at each point, are closely connected with the rapidity of the conduction, and they are also injuriously affected by anything which impairs it. It diminishes during the death of the muscle, and it is lessened also by fatigue, by cold, and by injury, such as excessive stimulation. Certain poisons also lessen it, as cyanide of potassium, veratrine, and upas antiar.2

Heat increases the rapidity of the conduction.