PREFACE TO THE SECOND EDITION 



Inquiby in the field of bacteriology is so active at the present day 

 that no general text-book can maintain its usefulness long without 

 frequent revision. In preparing the second edition of this book it has 

 been our purpose to correct omissions and to incorporate the more im- 

 portant researches of the last three years, rather than to alter exten- 

 sively the plan of the text. From the wealth of material which these 

 years have brought, we have attempted to glean those facts which 

 have seemed to us most important and most directly bearing upon 

 medical problems, since this book was planned, from the beginning, to 

 meet especially the needs of the student of infectious disease. 



The most extensive changes and additions have been made in the 

 chapters on streptococci, tuberculosis, plague, leprosy, syphihs, rabies, 

 and poUomyehtis. Short sections on typhus fever, on the plague- 

 like disease of rodents, and on rat leprosy have been added, and we have 

 inserted a tabulation of our knowledge of filtrable virus, adapted 

 largely from the summary recently published by Wolbach. The Ander- 

 son and McClintic method for the standardization of disinfectants, 

 and Churchman's recent work on anilin dyes and bacterial growth, 

 have been added. Many minor corrections and additions have been 

 made throughout the text. In preparing these changes, valuable as- 

 sistance has been given us by Dr. J. Gardner Hopkins, Associate in 

 Bacteriology at Columbia University, and many helpful suggestions 

 have been made by Drs. Dwyer and Bhss. 



It has been gratifying to note how much of the work which seemed 

 to us particularly valuable and enlightening has emanated, during these 

 three years, from American laboratories. 



We have purposely omitted making any extensive changes in the 

 section on immunity. The function of this part of the book is to give 

 the beginner a basis for further reading and introduce him, as simply as 

 possible, to the difficult problems of the field. We have felt that the 

 addition of much more detail and theory would render this section un- 

 suited to the needs of a general text-book. 



It is a sorrowful necessity that this revision must be put forth with- 



