44 MANUAL OF BACTERIOLOGY. 



Films of blood are prepared as directed in Chapter VII., Part 

 I., and are allowed to dry. 



(a) The stain is poured over the surface of the preparation 

 till it covers it. This serves to fix the fihn of blood. It is 

 allowed to remain for one minute. 



(&) Add distilled water, drop by drop, till a reddish tint 

 appears at the edges and a metallic scum forms on the surface. 

 About six drops are needed for a three-fourths inch cover-glass. 

 The real staining of the preparation now takes place, and 

 requires two or three minutes. 



(c) Wash in distilled water till the thin parts of the prepara- 

 tion have a yellowish or pinkish tint, which requires one to three 

 minutes . 



(d) Dry with blotting-paper and mount in Canada balsam. 

 Bacteria, malarial parasites, and cell-nuclei are stained 



blue, red blood-corpuscles are orange-pink, while the specific 

 granules of the leucocytes (neutrophilic, etc.) appear in various 

 tints from red to dark blue. The chromatin of the malarial 

 parasite takes a hlac to red color. The blood-plates have a 

 bluish or purplish color and must not be confused with malarial 

 parasites. 



The staining fluid is prepared as follows: To loo c.c. of a i per cent, 

 solution of sodium bicarbonate in water add i gram of methylene-blue. Place 

 in the steam sterilizer at ioo° C. for one hour. When cool add one-tenth per 

 cent, watery solution of eosin (Griibler, yellowish, soluble in water) until 

 the mixture loses its blue color, becomes purple, and a metallic scum forms 

 on the surface. About 500 c.c. of the eosin solution are needed. Collect 

 the precipitate on a filter; let it dry; make a saturated solution of the pre- 

 cipitate in methyl-alcohol; filter. To the quantity obtained add one-fourth 

 as much methyl-alcohol, so that the solution may not be completely saturated. 

 The purpose of the above procedures is to modify the methylene-blue so that 

 other staining elements are developed in it (polychromism). The modified 

 methylene-blue solution is then combined with eosin. For full details see 

 Wright. Journal oj Medical Research. Vol. VII. 1902. 



Staining of Spores. — The method is apphcable to cover- 



