vi PREFACE 



The chemistry of bacterial activity is not thoroughly studied at 

 the present time and many of its problems must await the develop- 

 ment of new methods of chemistry and physics, as well as a refine- 

 ment of existing methods. Nevertheless, sufficient information exists 

 to warrant its presentation in concrete form, partly to emphasize its 

 deficiencies, chiefly to indicate its relation to the biology of the bacteria, 

 which are potentially "living chemical reagents," as Professor Folin 

 has so aptly termed them. 



In the last analysis, the interest and importance of bacteria centers 

 around "what they do rather than what they are," and the elucida- 

 tion of this aspect of bacteriology lies largely within the field of 

 biochemistry. 



The relation of the chemistry of bacterial nutrition to the study 

 of intestinal bacteriology in health and disease is self-evident; some 

 of the more general aspects of this subject are briefly set forth in the 

 chapter relating to intestinal bacteria. 



It is with great pleasure that the writer acknowledges his indebted- 

 ness to his colleagues in the Northwestern Univeristy Medical School 

 for many valuable suggestions, to Doctors Noguchi and Amoss, of 

 the Rockefeller Institute, for the privilege of using the original plates 

 illustrating the Treponemata and Poliomyelitis, and to Mrs. N. M. 

 Frain for the line drawings in the text. Finally, the writer would 

 acknowledge his deep obligation to Miss Bertha J. Schwarz, Secretary 

 of the Department of Bacteriology, for her invaluable assistance in 

 the preparation of the manuscript and in reading the proof of the 

 book. A. I. K. 



CHICAGO, 1916. 



