Staining Bacteria in Tissues 179 



of difficulty, and the method employed must be modified 

 according to the particular kind of organism. The success 

 of the method will depend upon the good 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 

 immersed in absolute alcohol from six to twenty-four hours, 

 to kill and fix the cells and bacteria. The blocks are then 

 removed from the absolute alcohol and kept in 80 to 90 per 

 cent, alcohol, which does not shrink the tissue. Solutions 

 of bichlorid of mercury* may also be used and are par- 

 ticularly useful when the bacteria are to be studied in 

 relation to the cells of the tissues. 



Tissues preserved in 95 per cent, alcohol, Muller's fluid, 

 4 per cent, formaldehyd, and other ordinary solutions 

 rarely show the bacteria well. 



Embedding. The ordinary methods of embedding suffice. 

 The simpler of these are as follows : 



/. Celloidin (Schering). The solutions of celloidin are 

 made in equal parts of absolute alcohol and ether and 

 should have the thickness of oil or molasses. From the 

 hardening reagent (if other than absolute alcohol) pass the 

 blocks of tissue through: 



Ninety-five per cent, alcohol, twelve to twenty-four 

 hours ; 



Absolute alcohol, six to twelve hours; 



Thin celloidin (consistence of oil), twelve to twenty- 

 four hours; 



Thick celloidin (consistence of molasses), six to twelve 

 hours. 



Place upon a block of vulcanite or hard paraffin, allow the 

 ether to evaporate until the block can be overturned without 

 dislodging the specimen; then place in 80 per cent, alcohol 



* Zenker's fluid: 



Bichromate of potassium 2.5 grams 



Sulphate of sodium 1.0 gram 



Bichlorid of mercury . . . < 5.0 grams 



Water 100.0 " 



At the time of using add 5 grams of glacial acetic acid. Permit 

 the specimens to remain in the solution for a few hours only, then wash 

 for twenty-four hours in running water and transfer to 80 per cent, 

 alcohol. 



