PREFACE TO FOURTH EDITION 



The opportunity has been taken in this edition to revise each chapter 

 so as to incorporate as much as possible of what has been added to physi- 

 ological knowledge during the past two years. Certain chapters have 

 been rewritten, such as those on the output of the heart, the conditions 

 causing alterations in the acid base equilibrium of the blood, the normal 

 electrocardiogram and the movements and emptying of the stomach. 

 Considerable alterations have also been made in portions of other chap- 

 ters so as to permit of the incorporation of the recent work on intra- 

 cardiac pressure, the, capillary circulation, the mechanism of adaptation 

 to mountain sickness, pancreatic diabetes, etc. Several of the figures 

 appearing in earlier editions have been replaced by others of greater 

 usefulness. These alterations have been made without changing the 

 paging of the book. 



The author has again to thank Dr. N. B. Taylor for valuable assist- 

 ance in rewriting two of the chapters and in reading the proof. 



J. J. R. MACLEOD. 



Toronto, Canada, 

 1922. 



PREFACE TO THIRD EDITION 



Many changes have been made in the present (third) edition of the 

 book. The section on the nervous system has been entirely recast and re- 

 written by my colleague, A. C. Redfield, who, besides bringing this part 

 of the subject up to date, has incorporated with it an account of the 

 fundamental principles of neuromuscular physiology. Although no ap- 

 plication of this subject may at present be apparent in the investigation 

 of disease it is certain that such exists; but it can be made only after the 

 clinical researcher has become familiar with the brilliant work which 

 has been done in the field in recent years by Keith Lucas, Adrian, and 

 others. It is the function of a volume of this nature to describe not 

 merely what already has been achieved in the clinical applications of 

 physiology, but also to anticipate where this application is likely soon 

 to be made and to prepare the way by describing the physiological prin- 

 ciples that may be involved. 



Another section in which complete changes have been called for, is 

 that relating to the chemistry of respiration. This has been rewritten 



