84 BACTERIOLOGY 



The sections are transferred one by one to xylol, in order 

 to extract the paraffine from them, and are thence brought 

 into alcohol and then into water. If they do not sink in 

 the water the paraffine has not been completely removed, 

 and in this case they must be returned to the alcohol and 

 from that into xylol, and then transferred afresh to alcohol 

 and water. After removal from the water they are sub- 

 jected to suitable staining processes, cleared in xylol, and 

 mounted in xylol Canada balsam. Oil of cloves should 

 not be used for clearing the tissue, as it decolorises the 

 micro-organisms. 



In the preparation of serial sections a softer paraffine is 

 used for imbedding; the imbedding-block is otherwise 

 prepared in the same way as before and cut to a square, and 

 the microtome knife is fixed transversely. The sections, 

 which adhere to each other, forming bands which resemble 

 a tape-worm in outline, are laid one beside the other in 

 corresponding order and fixed to the slide, usually with the 

 white of a hen's egg diluted with water and glycerine. At 

 ordinary temperatures the white of egg takes a long time 

 to dry, but this may be expedited by gentle heating. A 

 drop of creosote or carbolic acid should be added to the 

 fluid to make it keep. Other fixing media are collodion, 

 glycerine agar, or glycerine gelatine in a dilute condition. 



The adherent pieces are freed from paraffine with xylol, 

 which is extracted in turn with alcohol ; they are then 

 washed in water, subjected to staining processes, rendered 

 transparent with xylol in the same way as single sections, 

 and put up in Canada balsam. 



ON THE STAINING OF SECTIONS 



The staining of sections is carried out after various 

 m3thods,but a certain order of procedure is common to all. 



