PREFACE TO THE FIRST EDITION 



WHILE a member of the Naval Examining Board and examiner in 

 bacteriology and clinical microscopy, I have during the past six years 

 had an opportunity to judge of the qualifications of several hundred 

 graduates of the various medical schools of the country from the stand- 

 point of practical application in the laboratory of that which they had 

 learned as undergraduates. 



More particularly I have made it a point to ascertain from the suc- 

 cessful candidates, while under instruction at the Naval Medical School, 

 the features of their laboratory courses, which had seemed to them 

 most practical; such methods being subsequently tested in our own 

 class work. 



As a result I have endeavored to incorporate in this manual methods 

 which have been submitted to the criticism of postgraduate students 

 from all the leading medical schools of the country, and which have been 

 considered by them adapted to the requirements of practical, speedy, 

 and satisfactory clinical laboratory diagnosis. 



For the laboratory worker the most valuable asset is common sense 

 and he must be able to bring to mind the possibilities of the production 

 of various artefacts and results from trivial errors in technic. It has 

 been my object to point out where such mistakes may arise, the reasons 

 for obtaining results differing from those ordinarily obtained and the 

 means employed to eliminate as far as possible such results. 



We are too apt to neglect the trivial details of stains, reaction of 

 media, and the like, yet it is only when every detail of technic has been 

 rigidly carried out that we are in a position to judge of the significance 

 of an object observed in a microscopical preparation. 



In bacteriology, candidates were frequently able to give the cul- 

 tural and morphological characteristics of all the important pathogenic 

 organisms, yet when it was required of them to outline the procedure 

 by which they would differentiate members of the typhoid-colon groups 

 when encountered in a plate made from faeces, the problem appeared 

 to them impossible. They possessed the information, but did not know 

 how to apply it. 



In practical work, organisms can only be separated culturally by the 

 use of Keys and for this reason Keys are given at the beginning of each 



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