GENERAL PRINCIPLES 161 



In such a medium, haemolysis (destruction of the red 

 blood-cells) is shown by a yeUow transparent halo around 

 the colonies. Organisms producing haemolysins, are : 

 Staphylococci, Streptococci, some Spirilla (but not Sp. 

 cholera) . 



STAINING REACTIONS AND METHODS. 



Saturated alcoholic solutions are kept as stock, and 

 diluted i in 10 with water as required, and filtered. 

 Rather use dilute stains and for a longer time, than have 

 precipitate of stain on preparation. Stains can be reduced 

 in intensity if necessary by using dilute acids, commonly 

 acetic i per cent. Acid stains, like eosin, stain the proto- 

 plasm of cells, whereas basic stains, like gentian-violet, 

 methylene-blue, and fuchsin, stain the cell-nuclei and 

 bacteria. 



Blood, pus, and smears from agar plates stain most 

 sharply with methylene-blue, but stain fades rapidly on 

 keeping. Certain bacteria need special stains. 



Loeffler's Methylene-blue. Saturated alcoholic solution 

 methylene-blue 30 c.c. ; solution KOH (o-oi per cent) 

 100 c.c. Keeps well. 



Aniline Oil-Water Stains. Made with saturated alco- 

 holic solutions of gentian-violet and fuchsin, which are 

 mixed i in 10 of aniline oil-water. The latter is a mixture, 

 made by shaking 5 c.c. of aniline oil in 100 c.c. distilled 

 water ; filter, and keep in dark. These keep badly. 



Carbol- fuchsin (Ziehl-Neelsen) . Ac. carbolic (5 per 

 cent) 100 c.c. ; saturated alcoholic solution fuchsin 10 c.c. 

 Diluted 3 to 4 times it stains more slowly but better. 

 Keeps well. 



Carbol-glycerin-fuchsin. Fuchsin i grm., ac. carbolic 

 liq. 5 c.c., glycerin 50 c.c., and aq. dest. 100 c.c. Dilute 

 in use 4 to 10 times. Keeps well. 



Carbol-methylene-blue. Methylene-blue 1-5 grm., abso- 

 lute alcohol 10 c.c., ac. carbolic (5 per cent) 100 c.c. 

 Keeps well. 



To Make a Film. Take a cover-slip (in Cornet's for- 

 ceps), and put on it a drop of distilled water (small for fear 

 of plasmolysis) . Take two strokes of culture with platinum 

 needle and rub into drop, and spread out. Dry in air 



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