AUTHOR'S PREFACE TO THE SECOND EDITION 



When the first edition of this monograph appeared, the circle 

 of those interested in this field was as yet small, and it gives me 

 pleasure to have contributed to the widening of this circle by means 

 of my little book. Since then, in spite of the external difficulties 

 of the years of war, such an enormous amount of work has been 

 performed in this field, that it would be beyond the power of a 

 single individual to render a complete account of all the details. 

 For better or worse I am obliged to sacrifice completeness of the 

 literature and to present the subject in text-book manner. The 

 scope had to be considerably enlarged, so that the second edition is 

 planned in several volumes of which the present first volume com- 

 prises the theoretical physico-chemical principles, while the follow- 

 ing volumes will present the methodology and the colloid-chemical, 

 physiological and medical applications. In this way a totally new 

 book will appear which has outgrown the scope of its title, and 

 which may be designated as a "second edition" only for the sake of 

 continuity with its small predecessor. 



The subject has been covered in the interval in several text- 

 books of physiology with various degrees of detail. The most nota- 

 ble monographic account is found in the book by W. M, Clark, 

 The Determination of Hydrogen Ions, Baltimore, 1920. This book 

 naturally has had a significant influence upon my second edition, 

 which influence will be evident in the volume on methods. 



The present first volume places the fundamental principles of 

 theory upon a wider basis than was done in the corresponding 

 section of the first edition. The cause for this lies in the first place 

 in the broadened realm of pure physical chemistry, and secondly 

 in the extraordinary growth of the multiplicity of applications of 

 this branch to the other branches of science. Therefore I deemed 

 it important to present to my biological readers the general theo- 

 retical principles upon a broad foundation, before the details of 

 their application are dealt with. 



Leonor Michaelis. 



Berlin, Christmas, 1921. 



