XXll INTRODUCTION 



The experience in this laboratory has been that the best 

 results are obtained by teaching the more fundamental prin- 

 ciples and methods as such before attempting to apply them 

 in the study of the various species of bacteria or in practical 

 diagnostic work. It has happened, even when the number 

 of exercises is very limited, that a preliminary drill in the 

 methods is greatly to the advantage of the student. From 

 the nature of the subject, its application can be made and 

 benefit derived therefrom only by those who know how to do 

 the things that the exigencies of the moment demand. This 

 means efficiency in knowing how. In following these direc- 

 tions, therefore, the student must understand that the purpose 

 of the first twenty exercises is to teach him how to do the 

 things called for in the later exercises in the study of species 

 and in some of the practical applications of bacteriology. 



Another feature of these directions is that they aim to teach 

 the student how to study and observe bacteria in their cul- 

 tures rather than to tell him what he is to observe. It is not 

 intended that they should take the place of lectures and text- 

 books in bacteriology. Their mission is to aid the student in 

 finding out for himself what the text-books relate concerning 

 certain species, and to guide him in the elementary steps in 

 the more important diagnostic procedures, tests, and analyses. 



The fact must also be recognized that in a short elementary 

 course it is not possible to try several methods for doing the 

 same thing. This restricts us to the use of a single pro- 

 cedure. The one is given that seems to us best adapted to 

 the limited time and facilities of the student. It may happen, 

 however, that other methods would be preferable under other 



