PREFACE TO THE FOUETH EDITION 



In this edition minor changes have been made. A few of the 

 experiments have been rewritten; some of the old methods have 

 been replaced by later, and it is hoped better, methods. 



The general plan of the book remains the same. Its object, as 

 heretofore, is to give adequate directions for the performance of 

 certain fundamental exercises in bacteriology. In attempting this 

 two considerations have been kept in mind, first, that in a rapidly 

 developing subject it is important that the directions for the 

 various exercises be worded so as to lend themselves readily to 

 changes which become desirable from time to time. With this 

 end in view the directions have been divided where possible into 

 a general and a special part. The general directions contain the 

 essential part of the exercise which does not permit of any con- 

 siderable variation, while the special directions embrace such 

 features as are most subject to modification, as for instance the 

 particular organism to be used, the kind of medium, the incuba- 

 tion temperature, etc. Desirable changes here are easily indi- 

 cated when the exercise is assigned ; second, that each experiment 

 should be complete in itself. Thus some of the experiments can 

 be performed in a few moments, while others require several days 

 for their completion. No attempt has been made to group them 

 into lessons. The order of the experiments is believed to be a 

 logical one, but may be readily adapted to meet the needs under 

 varying conditions. 



The various bacteria are studied in groups. This arrangement 

 is in keeping with recent tendencies, and it is hoped that it will 

 impress the student with the similarity between closely related 

 forms, and also emphasize certain minute but important differ- 

 ences. 



The system of classification adopted is that suggested by 

 Migula and is the one most widely accepted. 



The nomenclature used is determined by rules generally adopt- 

 ed by systematists. To those who still prefer the old names, the 

 synonyms will be found useful. 



(v) 



