94 PATHOGENIC BACTERIA. 



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. 



The ordinary methods of imbedding suffice. The sim- 

 pler of these are probably as follows: 



I. Celloidin. From the hardening reagent (if other 

 than absolute alcohol) 



12-24 hours in 95 per cent, alcohol, 



6-12 " " absolute alcohol, 

 12-24 ' thin celloidin (consistence of oil), 



6-12 " thick celloidin (consistence of molasses). 



The solutions of celloidin are made in equal parts of 

 absolute alcohol and ether. 



Place upon a block of dry wood, allow to evaporate 

 until the block can be overturned without dislodging the 

 spc-cmu-u ; then place in 70-80 per cent, alcohol until 



Mnm, l-vi). 1 6, 1896. 



