lo MICRO-ORGANISMS AND DISEASE [chap. 



place the excess of the dye is washed away with salt 

 solution, water or alcohol, or both, as the case may be (see 

 below). Unless the organisms are embedded in continuous 

 masses of solids, this method gives good results. In the 

 latter case, say if they are embedded in a microscopic lump 

 of tissue, or in a particular spot of a fine section of a fresh 

 tissue, it is necessary, after having placed the lump or 

 section on an object-glass, to drop the dye on to this previous 

 to putting on the cover-glass. After some minutes the dye 

 is allowed to run off by inclining the object-glass, and then 

 the washing is proceeclfd with till all the excess of the dye 

 is removed ; the mounting is then done by placing a drop 

 of water or salt solution on the specimen and covering 

 it with a cover-glass. In the case of sections through 

 fresh and hardened tissues containing micro-organisms, 

 the method of staining and of permanently mounting 

 them as a whole is more complicated, and will be detailed 

 presently. 



When one has to deal with coherent masses of micro- 

 organisms, present either in natural media {i.e. animal tissue) 

 or artificial cultivations, such as zooglea and pellicles of 

 micrococcus or bacillus, these can be bodily transferred to 

 a watch-glass, stained, washed, and mounted without much 

 difficulty, either for immediate or permanent use. The 

 permanent specimens are made in this way : — Place the 

 section or pellicle in a watch-glass containing the dye, leave 

 it there till deeply tinted, take out with a needle, section 

 lifter, or the like, wash in water, then in alcohol, leave 

 here for sufficient time till most of the excess of the 

 colouring-matter is removed, then lift it on to an object- 

 glass, spread well out, place on it a drop of xylol or clove- 

 oil, and after a minute or two drain off, add a drop of 

 Canada-balsam solution (in chloroform or xylol), and cover 



