vi PREFACE TO THE FOURTH EDITION 



current arc light was used and exposures were five to ten 

 seconds. Photographs of cultures are also original with a 

 few indicated exceptions. All temperatures are indicated 

 in degrees centigrade. 



For use of electrotypes or for prints furnished the author 

 is indebted to the following: A. P. Barber Creamery Supply 

 Company, Chicago, 111.; Bausch & Lomb Optical Company, 

 Rochester, N. Y.; Creamery Package Manufacturing Com- 

 pany, Chicago, 111.; Davis Milk Machinery Company, North 

 Chicago, 111.; Mr. C. B. Hoover, Superintendent of Sewage 

 Disposal Plant, Columbus, O.; Mr. C. P. Hoover, Super- 

 intendent of Water Filtration Plant, Columbus, O.; The 

 Hydraulic Press Manufacturing Company, Mt. Gilead, O.; 

 Loew Manufacturing Company, Cleveland, O.; Metric Metal 

 Works, Erie, Pa.; Sprague Canning Machine Company, 

 Chicago, 111.; U. S. Marine Hospital Service; Wallace and 

 Tiernan Company, New York City, N. Y. 



For the preparation of many cultures and slides, for great 

 assistance in the reading of proof and in the preparation of 

 the index, ]\Iiss Vera M. McCoy, Instructor in Bacteriology, 

 deserves the author's thanks. 



Exigencies of schedule have required a method of presenta- 

 tion of the subject different from that used with earlier 

 editions. This has resulted in rearrangement of the text-book. 



Some of the newer phases of bacteriology which have 

 become prominent since the last edition have been included— 

 the bacteriophage; mutation; life cycles; bacterial growth. 



x^dditions have been made to some portions of the text to 

 make the presentation more clear. A few figures are added 

 and some withdrawn. 



Professor Claude E. O'Neal of Ohio Wesleyan University 

 and Miss Florence Belle Darrah of State Teachers College, 

 Oshkosh, Wis., have offered valuable suggestions which are 

 hereby acknowledged. New material and new figures are 

 properly accredited in the appropriate places in the text. 



The author trusts that the book will find a place in College 

 and University courses in Bacteriology. 



C. B. M. 



Columbus, Ohio. 



