The author now offers, with all respect, but confidence, a few criticisms on the eminent investigators whose conclusions and methods he has been discussing. Madame Seiler was the writer who, as has been already said, brought more numerous and higher qualifications of a scientific and practical kind to the investigation of this subject than any other person. However, the study of physics, involving as it does the use of methods of extreme precision, tends to beget habits of mind which are not in all respects the best for the consideration of biological problems. Madame Seiler and her master, the physicist Helmholtz, regarded the vocal mechanism very much in the same light as they did their laboratory apparatus. Only in this way can the author explain some of Madame Seiler's positions; but on this assumption one can understand why she should make five registers, and consider them all, apparently, of equal importance. This latter, together with the tendency generally to present her views in too rigid a form, was, we think, her great error. Behnke admitted that all five registers might be heard, especially in contraltos, but he did not attach equal importance to each of these registers. Mackenzie the author conceives to have been misled by the very method that he considered a special virtue in his investigations--the examination of trained singers. Surely, if one would learn what is Nature's teaching on this subject, he must not draw conclusions from trained vocalists alone! By training one may learn to walk well on his hands, but this does not prove such a method the natural one, nor would it be good reasoning to draw this conclusion, even if a few individuals were found who could thus walk more rapidly than in the usual way. The diversity that Mackenzie found in singers does not, in the author's opinion, exist in nature; much if not most of it was due to training, and all that can be said is that several people may sing in different ways with not greatly different aesthetic results; but such methods of investigation may, as in this case, lead to conclusions that are dangerously liberal. The author holds to-day, as he did when he published his results many years ago, that "Impressions from general laryngoscopic observations or conclusions drawn from single cases will not settle these questions. Very likely differences such as these writers allude to may exist to a slight degree; but if they do, I question whether they are sufficiently open to observation ever to be capable of definition; nor is it likely that they interfere with methods of voice-production which are alike operative in all persons."