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 Second Edition, Tborougbly Revised PHILADELPHIA AND LONDON W. B. SAUNDERS COMPANY 1908 Reprinted, Set up, electrotyped, printed, and copyrighted, September, 1905. Copyright, 1907, by W. B. Saunders Company. Reprinted January, 1908, and October, 1908. PRINTED IN AMERICA PRESS OF W. B. SAUNDERS COMPANY PHILADELPHIA PREFACE TO THE SECOND EDITION. In the preparation of the second edition of this book the author has made no fundamental change in its arrangement or scope. Additions and changes have been made freely throughout the work, with the object of keeping the presentation of the subject abreast of the times, but as far as possible the additions have been counterbalanced by the elimination of such material as could be spared. The book remains, therefore, of practically the same. size, an object which the author has purposely kept in view, since he is convinced that in text-books there is a natural tendency to overexpansion which should be guarded against with care. New figures have been introduced whenever it seemed that an actual improvement could be effected by this means. The author has been gratified with the generous approval accorded to the first edition and hopes that the present edition may continue to find favor with teachers of physiology and medical students, as well as among physicians who may feel the need of keeping themselves in touch with the progress of physiology. There are, in fact, many indications that the physiological side of medicine is likely to receive a fuller recognition than has been given to it in the recent past. Medical schools are providing courses in experimental pathology and surgery, subjects in which physiological methods and training are all important, and in clinical medicine also it is becoming evident that the methods of physiological experimentation and the application of physiological discoveries are of practical value in diagnosis as well as in investigation. No one doubts that anatomy, physiology, and pathology, using these terms in a broad sense, constitute the basis upon which a rational system of medicine must be constructed, but it would seem that, in this country at least, the clinicians have failed to make full use of the material offered to them by the subject of physiology. Some explanation of this neglect is found in the fact that the physiologists themselves, not being practitioners, have no good |