METHODS OF OBSERVING BACTERIA. 149 



of the cover-glass to flood it, but not overflow, and is 

 allowed to remain for a moment or two, after which it 

 is thoroughly washed off with water. If the specimen 

 is one prepared for temporary use, it can be examined at 

 once, mounted in a drop of water, but under these con- 

 ditions will not appear as advantageously as if dried and 

 then mounted in Canada balsam. 



Sometimes the material to be examined is too solid to 

 spread upon the glass conveniently. Under such circum- 

 stances a drop of distilled water can be added and a minute 

 portion of the material be mixed in it upon the glass. 



The entire process is, in brief : 



1. Spread the material upon the cover ; 2. Dry — do not 

 heat ; 3. Pass three times through the flame ; 4. Stain 

 two to three minutes; 5. Wash thoroughly in water; 

 6. Dry; 7. Mount in Canada balsam. 



This simple process suffices to stain most bacteria. 



Ohlmacher 1 deserves credit for his observation that 

 when the " fixed " preparation is immersed for a moment 

 or two in a 2-4 per cent, solution of formalin, the brill- 

 iancy of the stain is considerably increased. 



Staining Bacteria in Sections of Tissue. — It not 

 infrequently happens that the bacteria to be examined 

 are scattered among or enclosed in the cells of tissues. 

 Their demonstration is then a matter of some difficulty, 

 and the method employed is one which must be modified 

 according to the kind of organism to be stained. Very 

 much, too, depends upon the preservation of the tissue 

 to be studied. As bacteria disintegrate rapidly in dead 

 tissue, the specimen for examination should be secured 

 as fresh as possible, cut into small fragments, and im- 

 mersed in absolute alcohol from six to twenty-four hours 

 to kill the cells and bacteria. Afterward they are re- 

 moved from the absolute alcohol and kept in 80-90 

 per cent., which does not shrink the tissue. Bichlorid 

 of mercury may also be used, but absolute alcohol seems 

 to answer every purpose. 



1 Medical News, Feb. 16, 1896. 



