viii INTRODUCTION. 



practice and the science upon which practice should be founded are 

 amalgamated. The practical man in Agriculture too frequently is so 

 extremely traditional in his practice that he utterly fails to separate 

 the true from the false, or, in other words, does not exercise his discrimi- 

 native powers at all, but depends entirely upon so-called haphazard 

 methods and self-willed processes. This factor in agricultural education 

 operates against the proper development and logical study of any branch 

 of science in its relation to the farmer. 



The plan of a text-book in Microbiology which seeks to furnish basic 

 principles, to train the mind in logical development and adjustment, 

 and to prepare the student to undertake an intelligent study of strictly 

 professional or practical subjects, must assume a definite and systematic 

 arrangement. With this in mind, the text has been divided into three 

 distinct parts: Morpholog'cal and Cultural, or that which deals with forms 

 and methods of handling; Physiological, or that which deals strictly with 

 functions, the key to the applied; Applied, or that which reaches into the 

 application of the facts developed to the problems met in the study of 

 professional or practical affairs of Agriculture or Domestic Science. 



In presenting this text-book, the product of several hands, there is 

 the most serious difficulty in obtaining unity of thought and expression 

 without repetition; besides, that very conspicuous weakness of emph- 

 asizing some features unduly while other features of importance are 

 scarcely mentioned, confronts us. A most earnest attempt has been made 

 to overcome these faults as far as possible, but a complete mastery of them 

 cannot be expected in the first product. However, what is lacked in unity 

 and continuity of expression and in balance, we sincerely hope will be 

 made up, in part at least, by the selection and the value of the material 

 contributed. 



Laboratory features of microbiology have been eliminated wher- 

 ever it has been practicable. Should any demonstrations be added 

 or needed, we have felt that they may be easily supplied by the instructor, 

 who, of course, will be governed by local facilities and conditions. Al- 

 though no space has been given to laboratory exercises, it should not be 

 gathered that the authors of this book are any the less earnest in urging 

 a well-organized laboratory course to supplement the general instruction 

 as an essential factor to a working appreciation of the subject. 



In matters of spelling, new words, and phrases, conservatism has 

 controlled. Arbitrary decisions and selections have been forced in 



