i.j MICROSCOPIC EXAMINATION. 5 



first instance the process is carried out thus : A microscopic 

 specimen is made, and to it is added afterwards drop after drop 

 of the dye, passing it through the specimen in the usual way 

 of applying fluids to a microscopic specimen, i.e by adding with 

 a capillary pipette the dye at one margin of the cover-glass and 

 sucking it up with a strip of filter-paper applied to the opposite 

 margin of the cover-glass. When the staining has taken 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 particu- 

 lar 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 proceeded 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 speci- 

 men and covering it with a cover-glass. In the case of sections 

 through fresh and hardened tissues containing micro-organ- 

 isms, 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-organ- 

 isms, present either in natural media (i.e. animal tissue), or arti- 

 ficial cultivations, such as zoogloea and pellicles of micrococ- 

 cus or bacterium, 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 sections or pellicle in a 

 watch-glass containing the dye, leave it there till deeply tinted, 

 take out with a needle or "the like, wash in water, then in 

 alcohol, leave here for five minntes or more 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 clove-oil, 

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

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

 with a cover-glass. In some special instances such as the 

 bacilli of leprosy and tuberculosis, double staining is required. 

 With other organisms, such as the bacilli of glanders or 

 tuberculosis, the washing is carried out, not with water 

 but with acid (acetic acid and nitric acid respectively). All 

 the details will be stated when dealing with these special 

 organisms. 



