OF PHYSIOLOGY FOR MEDICAL STUDENTS AND PHYSICIANS BY WILLIAM H. HOWELL, PH. D., M. D., LL. D. PROFESSOR OF PHYSIOLOGY IN THE JOHNS HOPKINS UNIVERSITY, BALTIMORE Tbird Edition, Tborougbly Revised PHILADELPHIA AND LONDON W. B. SAUNDERS COMPANY KF 9395 Ap.7,1911 HARVARD UNIVERSITY, To replace cufiny lost. IN VERS 47*95 Copyright, 1905, by W. B. Saunders and Company. Reprinted February, 1908, and October, 1908. Revised, reprinted, Copyright, 1909, by W. B. Saunders Company. Registered at Stationers' Hall, London, England. Reprinted January, 1910, and July, 1910. PRINTED IN AMERICA PRESS OF W. B. SAUNDERS COMPANY PHILADELPHIA PREFACE TO THE THIRD EDITION. In the short interval of two years which has elapsed since the preparation of the second edition of this text-book a large amount of new material has been added to the literature. To the author it has seemed, in fact, that there has been an unusual wealth of contributions to our knowledge, both as regards facts and new points of view. This material is scattered through a wide range of publications, for the tendency toward the multiplication of special journals shows no signs of abatement. No one would be justified in claiming that he had winnowed all of this extensive field. The author has attempted to scrutinize the sources of information which are recognized as specifically physiological, but he is conscious that much of direct interest to physiology now appears in journals nominally devoted to other subjects, and which, therefore, is liable to be overlooked for a time by the professional physiologist. As it is, the labor of revision has been very great, and numerous additions and corrections have been made in many parts of the book. In the second edition most of the changes incorporated were made necessary by the valuable results following upon the extensive application of chemical methods of investigation. In the present edition, the new facts that have been added, as a consequence of improvements in the methods of socalled physical physiology, are perhaps as important as those that we owe to the use of the chemical methods. It requires but little acquaintance with the development of physiology as a whole to realize that all good methods of investigation, whether physical, chemical, or anatomical, have now as formerly an abundant opportunity of attaining results of the greatest importance. While most of the changes made in the present edition have been of the nature of the correction or modification of former statements, or the addition of new facts, the author has not hesitated at times to include also brief mention of new theories or points of view, which, while possibly of only temporary importance, are at least characteristic of the present stage of development of the subject. |