THE lymph of reptiles and amphibia is returned to the blood circulation by the action of actual lymph hearts.1 Lymph hearts, as such, do not occur in mammals, and the source of the energy that is necessary to return the lymph to the bloodstream is still the subject of debate. Broadly speaking, there are two schools of thought. The "traditional" view, which finds expression in the standard reviews,2 , 3 is that extralymphatic sources of energy, such as the movements of skeletal muscles and the pulsations transmitted from arteries, fortuitously compress the valved lymphatic vessels and thus force the lymph in a . . .