160 BACTERIOLOGY. 



minutes. They are then removed, rinsed in water, and 

 partly decolorized in 0.1 per cent, solution of acetic acid for 

 only a few seconds ; again washed out in water, then in 

 absolute alcohol for a few seconds, and from this again 

 into absolute alcohol for the same time, and finally into 

 cedar oil or xylol. Here they remain for from one-half to 

 three-fourths of a minute. They are now to be carefully 

 spread out upon a spatula, which is held in the fluid 

 under them, and, without draining off the fluid, are trans- 

 ferred to a clean glass slide. This must be done care- 

 fully to avoid tearing. The easiest way to do this is to 

 hold the spatula on which the section floats in one hand, 

 with its point just touching the surface of the glass slide, 

 and then with a needle pull the section gently off upon 

 the slide. The fluid comes with it, and the floating sec- 

 tion may be easily spread out into a flat surface. The 

 excess of fluid is taken up with blotting-paper, after 

 which a drop of xylol-balsam is placed upon the centre 

 of the section, and is then covered with a thin, clean 

 cover-slip. It is now ready for examination. 



Each step in the above process has its definite object. 

 The sections are placed in water before staining in order 

 that the diffusion of the straining solution into the tissues 

 may be diminished ; otherwise our efforts at rendering 

 the bacteria more conspicuous by decolorizing the tissues 

 in which they are located would rob the bacteria of 

 their color as well. 



The acetic acid and also the alcohol are decolorizers, 

 and are directed toward the excess of staining in the 

 tissues. The cedar oil or xylol are bodies which mix 

 on the one hand with alcohol, on the other with balsam. 

 They are known as " clearing fluids," and not only serve 

 to differentiate the component parts of the tissue but fill 



