INTRODUCTION xix 
conditions or in the hands of certain individuals. This limi- 
tation is a necessity, however, in an elementary course of 
instruction. Its objection is partially met by references to 
text-books and other publications where additional methods are 
described. It is very important that the student familiarize 
himself with at least a few of the more important books and 
periodicals dealing with bacteriology and protozoa. They are 
the source to which he must go later for information on this 
subject, and consequently a knowledge of their nature and how 
to use them may be of unmeasured value. 
The introduction of methods for the specific diagnosis of 
the more common infectious diseases of animals will, it is be- 
lieved, be of much’value to practitioners, especially after they 
have had the exercises as students. 
