FIXING OF TISSUES 115 



4. Use on fixed cover-glass or slide preparation at once and allow 

 the stain to act not less than one hour, better several hours. 



5. Wash well in water, dry carefully between filter paper, and 

 mount in Canada balsam. 



If precipitates have been formed on the specimen it is well to 

 wash rapidly a few seconds in 90 per cent, alcohol and then once 

 more stain a short time in the dilute Giemsa stain, without the addi- 

 tion of carbonate of potash, i. e., a drop of the stain to each cubic 

 centimeter of pure distilled water. 



Blackening of the Background for Demonstration of Fine Spirochetse. 

 Freudenwald has published recently a method of demonstrating a 

 few fine spirocheta? (particularly the Spirochsetse pallida) in secretions 

 which may contain them. The procedure is not a staining method, 

 but one in which a dark background is prepared by the use of Chinese 

 (India) ink, upon which the microorganisms appear as light un- 

 stained spiral threads. The method is as follows: 



1. Take a platinum loopful of the discharge which is suspected 

 of containing the microorganisms. 



2. Mix and rub it up well with a drop of Chinese ink on a clean 

 slide (the author recommends a German preparation fluid Chinese 

 ink of Guenther and Wagner). The mixture assumes a yellowish- 

 brown tint. 



3. Spread the drop out into a thin film with the margin of another 

 clean slide and allow it to become air dry. 



4. The preparation can now be directly examined with the oil- 

 immersion lens. If the specimen has been well spread in a thin layer, 

 the spirochetae appear perfectly white on a yellowish or yellowish- 

 brown background. After examination the homogeneous immersion 

 oil can be washed off with xylol and the preparation can be pre- 

 served as a permanent one for future use. The author has found 

 this new method very simple and giving very excellent results. Any 

 India ink may be used. It is not necessary to procure the German 

 preparation originally recommended. 



Staining Bacteria in Tissues. It is often desirable and necessary 

 to study the distribution of bacteria in tissues. In order to do this 

 successfully the tissues must first be properly fixed, embedded, and 

 sectioned. 



Fixing of Tissues. Fixing a tissue means its preservation by proper 

 preserving fluids so that its cells and other elements remain as nearly 

 true to nature as possible. Pieces not larger than one cubic centi- 

 meter must be cut out with a sharp scalpel or razor. These pieces are 

 dropped at once into strong or absolute alcohol, a formalin solution 

 (1 part of formalin to nine parts of water), or best, if certain stains 

 are to be used, into Zenker's solution. 



Bichromate of potassium ... 2.5 grams 



Sulphate of sodium . . . -. . . . ..... . 1.0 gram 



Corrosive sublimate . . ... . ....... .5.0 grams 



Water . 100 c.c. 



