PREFACE 



THE manuscript of this book was completed for publi- 

 cation in 1915 and, in general, that year may be taken as the 

 date of the outlook, but here and there, where it seemed most 

 necessary, it has been revised down to the end of 1919. 



Those who seek for completeness in these pages will not 

 find it. The book is in no senes a monograph, but only, as its 

 title indicates, an introduction to the subject. 



While the book has been made primarily for laboratory 

 use under the guidance of a competent teacher, who will add to 

 it or subtract from it as he desires, it is believed that many 

 persons not students may find in it various things of interest, 

 and partly with this wider public in view it has been illustrated 

 very fully. 



This book is the result of 35 years of reading and 25 years 

 of diligent laboratory and field investigation. More than 

 most books, it is the product of experiment. There is scarcely 

 a line or a statement in it that has not required more than one 

 experiment. It is also largely the product of a single labora- 

 tory, that is to say, 8 of the 14 organisms here selected for 

 special study w T ere named by the writer (one with a colleague), 

 two were worked out by others in his laboratory (Bacillus 

 carotovorus and Bacterium maculicolum) , and of the remaining 

 four, all of Appel's statements have been verified with addi- 

 tions under Bacillus phytophthorus, many additions have been 

 made to Pammel's statements under Bacterium campestre, 

 the entire body of description has been worked up for Bacterium 

 mori, and some additions have been made to Bacillus amylovorus. 

 Moreover, all but 35 of the 650 illustrations are from this 

 laboratory. 



A majority of the photographs in the book \vere made 

 by James F. Brewer and the remainder by the writer. Fre- 

 quently we worked together. In case of particularly good 



