. 



MICROSCOPIC EXAMINATION. 475 



merit until the lens just touches the oil; then it is accurately adjusted 

 upon the preparation with the micrometer screw. 



(a) Unstained preparations. Narrow diaphragm ! They are exam- 

 ined in two ways : 



1. A drop of pure culture in a fluid medium or a little drop of water 

 with a trace of pure culture mixed in it is placed between the slide 

 and cover-glass; or, better, 



2. In a hanging drop. A drop of a pure culture in a fluid medium 

 r a drop of bouillon in which is mixed a minute quantity of a pure 



culture is placed upon a cover-glass; the cover-glass is then turned over 

 and placed upon a hollow ground slide so that the drop is suspended 

 within the hollow. The cover-glass is now fixed to the slide by apply- 

 ing a very little water to each corner of the cover, or, if the observa- 

 tion is to be more prolonged, by means of vaselin. 



(b) Stained preparations. Open diaphragm ! Abbe's illuminating 

 apparatus. In the examination of sections with a double stain, the 

 wide diaphragm is required for the bacteria, the narrow opening for 

 the tissues. 



(C) Cleaning the Preparations and the Microscope. — The 

 immersion oil is always gently brushed off, and now and then quickly 

 cleaned with xylol and chamois skin ; the setting of the lens is loosened 

 by prolonged action of the xylol. Also immersion oil dried upon the 

 cover-glasses of old preparations is readily removed by xylol. 



2. The most Important Solutions for Use in Making 

 Preparations. 



(A) Staining Solutions. 



i. Aqueous Alcoholic Solutions of Fuchsin and Methylene- 

 blue. — A concentrated " stock-solution " is prepared by pouring abso- 

 lute alcohol upon the pulverized dyes (fuchsin, methylene-blue) in 

 bottles, and after shaking and allowing them to stand a few hours, 

 they are filtered. Of this saturated solution 1 part is mixed with 4 

 parts of distilled water, and before using is filtered. In order to 

 obtain good preparations it is better to stain a longer time with weaker 

 solutions than for a short time with strong solutions. 



2. Carbol-fuchsin (Ziehl's Solution). — 



Fuchsin 1.0 gm. 



Acid, carbolic, liq 5.0 " 



Alcohol 10.0 " 



Aq. dest 90.0 " 



3. Anilin Fuchsin. — Four parts of anilin oil (anilin. pur.) are well 

 shaken several minutes with 100 parts of distilled water, and then fil- 

 tered until all the water has passed through clear ( then the funnel is 

 removed, since otherwise oil will also pass through). In this anilin 

 water 4.0 gm. fuchsin are dissolved and it is again filtered. 



4. Anilin Gentian-violet (Ehrlich's Solution). — To 100 c.c. of 

 anilin water, 11 c.c. of a concentrated alcoholic solution of gentian- 

 violet (stock solution) is added. This solution does not keep long. 



