Cough may be either a voluntary or an involuntary act; perhaps most often it is an involuntary act reinforced by volition. Semicough,1commonly called "clearing the throat" and expressed in lay literature as "ahem," is always voluntary, though nerve-cell habit may make it an almost subconscious act. It is only the involuntary cough of purely reflex character that will be considered here. The following brief and clear statement of the physiologic mechanism of cough by my colleague Prof. Albert P. Brubaker is authoritative: "The cause of the cough is an irritation in the area of distribution of the glossopharyngeal, the trigeminal and perhaps other sensory nerves as well. In the unconditioned or purely reflex cough, the local irritation develops nerve impulses which are transmitted by the vagus from the air passages." My colleague Dr. F. J. Kalteyer, in a personal communication, calls my attention to the fact that MacKenzie