CHAPTER II. 



Methods of Investigation; the Microscope; Microscopical Examination of 

 Bacteria; Stains and Staining; Preparation of Cover-Glass Specimens for 

 Staining. 



METHODS OP INVESTIGATION. 



In order to learn the peculiarities of tlie bacteria, to become ac- 

 quainted with their nature and habits, the only means at command 

 for a long time was to examine them microscopically in the state 

 in which they occar in nature under ordinary conditions. 



This was a very imperfect procedure, the more so as the micro- 

 scope itself was inadequate for our purposes. Of these smallest 

 living forms little could be seen with the aid of the strongest ob- 

 tainable magnifying power, and this little was so peculiar that we 

 had great difficulty in comprehending it. It was not till a later 

 period that we learned to render the bacteria more accessible to 

 observation by special preparation and staining processes. 



Microscopic examination, both of unstained and of stained 

 micro-organisms, is still an indispensable and essential part of bac- 

 terial investigation, and in the decision of the great majority of the 

 questions that arise it plays an important part. 



Yet we are no longer dependent on the microscope alone for our 

 knowledge of bacterial life, and the rapid progress made in bac- 

 teriology in the last few years dates from the moment when we 

 began to detach the bacteria from the accidents and casualties of 

 their natut-al existence, to breed them artificially under favorable 

 conditions, and to study their behavior under given circumstances. 



Microscopic examination and the breeding process work hand in 

 hand in the most satisfactory manner, and open to us, in some 

 cases, a really deep insight into the mysterious and various mani- 

 festations of the lowest representatives of organic life. 



Yet, that with all these improved means of research we have by 

 no means reached the desired goal, is shown by the simple fact that 

 even the best-known species of micro-organisms still present an 

 abundance of unexplained phenomena. 



