41 phenomenon made up by a systole of the heart of the condition of tension of the auriculo-ventricular valves. Surely the mus- culi papillares will contract with the rest of the ventricular walls, and, contracting, will they not stretch the chordae tendineae and the valves'? For myself, I would say that we are more likely to overrate the share taken by the valves than to underrate that taken by the muscular walls. I need not say to this audience that the fact with which we are all familiar, of the alteration in the first sound produced by disease of the auriculo-ventricular valves, does not absolutely prove that they produce any part of it during health ; and, finally, to my own ear at least, a modification of Wollaston's experiments, which anybody can try for himself by making his temporal and mas- seter muscles contract at any time of perfect stillness, appears to produce a sound which is scarcely, if at all, different in quality from the first sound of the heart. A judgment, however, upon the nature of a sound, or, indeed, an aggregation of sounds, as in music, is one upon which two observers may
