The most peripheral lymphatic vessels of rats, mice, and guinea pigs were found to possess a spontaneous intermittent contractility. (a) The rate of contraction was shown to be directly proportional to the rate of formation of lymph and contractions were apparently initiated by an increase in intraluminal pressure. (b) Epinephrine and pituitrin caused an increased contractile rate, or lymphatic spasm, whereas novocaine caused cessation of movement and lymphatic dilatation. (c) Section or electric stimulation of femoral and sciatic nerves did not alter the contractile rate of popliteal lymphatics.

This spontaneous lymphatic contractility was not observed in rabbits and dogs although the lymphatic vessels did contract when irritated. Epinephrine, pituitrin, and novocaine produced the same effects as observed in the smaller mammals. Dilatation of lymphatic vessels produced by intradermal injection of fluid, massage, or passive motion was followed by a rapid return of the vessel to normal caliber.

The frequency of valves in lymphatic vessels, the distensibility of the lymphatics, and their ability to return to normal caliber against an increased gradient of pressure are considered to be the essential elements of an intrinsic mechanism contributing to the transport of lymph.

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