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 funda- 

 mental principles of neuromuscular physiology. Although no applica- 

 tion 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 principles 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 and 

 rearranged so as to incorporate the recent work on the effects of deficiency 

 of oxygen on the respiratory center, as well as the interesting and important 

 clinical applications of the subject. Several new chapters have been added 

 dealing with such practical problems as the measurement of the functional 

 capacity of the heart, the principles of ventilation and the therapeutic 

 value of oxygen, and the chapters on vitamines, on the capillary circula- 

 tion, on surgical shock, and on the interpretation of polysphygmograms 

 have been rewritten. 



In practically every other section of the book many additions have 

 been made, particularly in that which deals with the endocrine organs, 

 and several new figures and tables have been added. To make room for 

 these changes some of the more technical details, appearing in the previous 

 editions, have been put in small print and some of the figures removed. 

 This has been done in order to keep the volume as near to its original 

 bulk as possible. 



I wish to take this opportunity to thank my colleagues here and else- 

 where for many valuable suggestions and for their encouraging comments 

 on the book. I am also greatly indebted to Dr. N. B. Taylor for his as- 

 sistance in the preparation of this edition and for reading the proofs. 



J. J. R. MACLEOD. 



Toronto. Canada. 

 1920. 



