THE STAINING OF BACTERIA IN TISSUES. loi 



we take one piece out, leaving the remainder in soak 

 for future use. We now take a wide-mouthed bottle, 

 with a well-fitting cork stopper, on to which we fasten 

 the piece of material with a needle. The bottle is then 

 filled with absolute alcohol, so that when the cork is 

 replaced, the piece of spleen is completely immersed. 

 The alcohol gradually abstracts the water from the 

 tissue, and as that containing the water sinks to the 

 bottom, fresh alcohol continually comes in contact 

 with the material. The alcohol is changed on the 

 next day, after which as a rule the specimen is thor- 

 oughly hardened, and suitable for being cut up into 

 sections. Sometimes it is not necessary to put fresh 

 alcohol, but on the other hand it is sometimes neces- 

 sary to change it a second time. This difference is 

 caused partly by the varying capacity of the alcohol 

 for holding moisture, and partly by the varying amount 

 of water contained in the tissue. Tissues containing 

 much water are of course more difficult to harden than 

 those containing little. 



When the pieces of spleen are sufficiently hardened, 

 they are taken out of the alcohol and cut up into 

 halves, if the sections are to be made with a microtome. 

 One of these halves, five millimetres thick, is then 

 stuck by one of its broader sides on to a cork, which 

 can be securely fixed into the clamp of the microtome. 

 It is best to use a solution, of gum for stickino- it on, 

 after the alcohol has evaporated. The piece is pressed 



