94 PA THOGENIC BA CTERIA. two to three minutes; 5. Wash thoroughly in water; 6. Dry; 7. Mount in Canada balsam. This simple process suffices to stain most bacteria. Ohlmacher1 deserves credit for his observation that when the u 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 tl u absolute alcohol, 12-24 u u ^hin celloidin (consistence of oil), 6-12 u u 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 specimen ; then place in 70-80 per cent alcohol until 1 Medical News, Feb. 16, 1896.