138 The Microscope. 



SELECTIONS. 



THE STAINING OF BACTERIA FOR MICRO-PHOTO- 

 GRAPHIC PURPOSES. 



BY EDGAR THURSTON, 

 CURATOR OF THE ANATOMICAL MUSEUM, KINGS COLLEGE, LONDON. 



By means of micro-photography, very faithful representa- 

 tions of the form and general grouping of bacteria can be repro- 

 duced, such as it is exceedingly difficult to delineate in a draw- 

 ing, however artistically it may be executed. At the hands of 

 only a few men has, however, the photographing of bacteria 

 been really successful, and one too frequently sees the organ- 

 isms represented as faint, indistinct bodies with ill-defined out- 

 line, and surrounded by a hazy zone, the first fault being due to 

 unskilled execution of the staining processes, and the second to 

 the employment of indifferent objectives and bad illumination 

 of the object; on both which points special care must be be- 

 stowed, as nearly all bacteria require for their investigation 

 high-power objectives. 



Micro-photography, in its application to bacteria, must be 

 dealt with under two headings : 1st, the preparation of the bac- 

 teria by suitable staining methods ; 2nd, the process of photo- 

 graphing them ; and I propose on the present occasion to deal 

 with only the former. 



It may be required to photograph bacteria under two dis- 

 tinct conditions, according as they are present — 1, in the free 

 state or in fluids; 2, in the organs and tissues of the animal 

 body ; and for each of these conditions a special mode of prep- 

 aration must be adopted. 



As examples of bacteria occurring in a free state, or in 

 fluids, I may take, from among many, the various colored 

 (chromalogenous) species of which colonies grow on the sur- 

 face of eggs, meat, bread or potatoes ; the putrefactive bacteria 

 in decaying meat or vegetable infusions ; the sputum (expec- 

 torated matter) from the lungs of a pneumonic or tuberculous 

 person ; or the blood of an animal suffering from splenic fever. 



To stain such bacteria the following mode of procedure will 

 be found the best: Place a minute portion of the bacterial fluid, 



