METHOD OF STAINING SPECIMENS. 35 



simply allowed to, run off by standing the cover-glass slant- 

 wise against an object. When the specimen is to be examined 

 in water (which is always best with the first preparation of 

 the specimen, as the Canada balsam destroys to some extent 

 the natural appearance of the bacteria), a small drop of ster- 

 ilized water is placed upon the glass slide, and the cover-glass 

 dropped gently down upon it, so that the cover-glass remains 

 adherent to the slide. 



The dry system or the oil-immersion can now be used. 



When the object has been sufficiently examined it can be per- 

 manently mounted by lifting the cover-glass off the slide (this 

 is facilitated by letting a little water flow under it, one end 

 being slightly elevated). The water that still adheres is dried 

 off in the air or gently over the flame, and when perfectly dry 

 it is placed upon the drop of Canada balsam which has been put 

 upon the glass slide. 



In placing the cover-glass in the staining solutions one must 

 be careful to remember which is the spread side. 



By holding it between yourself and the window, and scraping 

 the sides carefully with the sharp point of the forceps, the side 

 having the specimen on it will show the marks of the instrument. 



Little glass dishes, about one-half-dozen, should be at hand 

 for containing the various stains and decolorants.. 



Tissue Preparations. In order to obtain suitable specimens 

 for staining, very thin sections of the tissue must be made. 



As with histological preparations, the tissue must be hardened 

 before it can be cut thin enough. Alcohol is the best agent for 

 this purpose. 



Pieces of the tissue one-quarter inch in size are covered with 

 alcohol for 24 to 48 hours. 



When hardened it must be fixed upon or in some firm object. 

 A paste composed of 



Gelatine ...... 1 part. 



Glycerine 4 parts. 



Water 2 parts. 



will make it adhere firmly to a cork in about 2 hours, or it can 

 be imbedded in a small block of paraffine, and covered over with 

 melted paraffine. 



