PREFACE. 
In the following pages the attempt has been made 
to group together those facts in Bacteriology which 
will constitute a sufficient text-book for the student and 
which are of direct practical value to the physician 
and health officer. Laboratory technique is given in 
its essentials and to such an extent as is necessary to 
make bacteriological methods plain to the physician, 
to guide him in making the simple examinations pos- 
sible in his office, and to show him under what 
conditions he can obtain diagnostic or other help from 
bacteriological examinations in laboratories. The phy- 
sician can readily understand and apply the essentials 
of bacteriology, but the actual carrying out of the 
more difficult examinations should be left to the 
trained bacteriologist. 
Such subjects as the chemical changes produced by 
bacteria, infection, immunity, the nature and use of 
protective serums, and the diagnostic value of bacte- 
riological cultures, are particularly emphasized, since 
knowledge of such subjects is of special importance to 
