VIU PEEFACE 



study each function in itself and in its effect upon the 

 other functions. This study is limited to the necessary 

 functions of life; therefore, motility, phosphorescence, 

 tropisms, and similar conspicuous but unimportant 

 functions have been omitted. 



By confining the discussion to the indispensable functions 

 of the simplest forms of life, I hope to arouse an inter- 

 est for this kind of work not only among bacteriologists, 

 but among plant and animal physiologists as well. 

 While practically all the discussion in the book refers 

 to bacteria, the principles developed reach beyond the 

 domain of bacteriology, and apply to biology generally. 

 More than that, I believe that some of the principles 

 of biology can be found and studied only with the 

 simplest forms of life, and that general physiology has 

 much to learn from the physiology of bacteria. 



This book is not intended to be a review of literature 

 on the subject. Such compilations exist already in the 

 books mentioned above. It contains a number of 

 unpublished experiments made with the object of 

 deciding certain doubtful points in physiology. 



The work is meant to be critical. I have tried to 

 present all theories, and to mention their strong and 

 weak points. To counterbalance any personal view- 

 point, each chapter and subchapter contains a summary, 

 usually separated according to facts and theories. 



An effort has been made to separate logically, and, if 

 possible, experimentally, growth from fermentation; 

 also to differentiate between the rates of the processes 

 and their end points. Many arguments on growth have 

 arisen because one investigator measures growth by 

 generation-times and another by the maximum number 

 of cells produced. No new definitions are required; no 

 new words have to be coined to distinguish between rates 



