PREFACE. 
No practitioner who wishes to do his best for his 
patients and to promote his own interests can afford to 
neglect any means of clinical investigation which may 
help him to arrive at a correct diagnosis, and offer hints 
as to prognosis and treatment. Pre-eminent among the 
more recent methods of investigation are those which 
are applied by the bacteriologist; and it is no exaggera- 
tion to say that in many of the infective diseases a 
diagnosis which is made without a_bacterioscopic 
examination is either mere guess-work or can only be 
made so late that the patient has suffered unnecessarily 
in health and the practitioner in prestige. In many 
cases, however, the investigation requires a consider- 
able amount of technical skill and access to a well- 
equipped laboratory; the former may perhaps be pos- 
sessed by the rising generation (for bacteriology is now 
an integral part of the medical curriculum), but it 
would be unfair to expect every medical man to add 
the latter to his already expensive equipage. But in 
many cases the diagnosis can be arrived at by very 
simple means—a few slides, cover-glasses, and stains, 
a good microscope (which ought to be considered as 
essential as a stethoscope), and a very moderate amount 
of technical skill will often enable the practitioner to 
arrive at correct diagnosis in a very short time. This 
little book is intended in the first instance to show 
exactly when this may be done, and to provide clear, 
succinct, and full descriptions of simple methods which 
may be employed. ‘The descriptions of the operations 
which the practitioner can carry out for himself are 
mostly written in the imperative mood, and are in- 
tended to be referred to constantly and carried out, step 
by step, during the process. They represent the in- 
