98 PHARMACEUTICAL BACTERIOLOGY 



teria are fixed or embedded. Acidulated (with HCl) alcohol is most 

 commonly employed. Ordinarily, rinsing in a small stream of water is 

 sufficient. Some bacteria resist the decolorizing process with acids more 

 strongly than others, and are said to be acid fast or acid proof, as, for 

 example, the bacilli of leprosy andof tuberculosis, while the great majority 

 of species give up the stain very readily. It is a fa ct that one and the same 

 species of microbe reacts variably with one and the same stain, depending 

 upon a variety of causes. Moderate heat hastens and intensifies the 

 staining. 



For ordinary purposes a single stain only is used, but sometimes struc- 

 tural differences are more clearly shown by what is known as double or con- 

 trast staining. Take, for example, a spore-bearing microbe, as that of 

 anthrax. The spores may be stained by means of carbol fuchsin; the en- 

 tire cell, excepting the spore, can be completely decolorized in acidulated 

 alcohol, and then methylene blue or gentian violet applied as the contrast 

 stain. We then have a blue cell-wall with a red spore. However, the 

 beginner is apt to be disappointed in his attempts at double staining. 



The pharmacist will have comparatively little to do as far as the actual 

 staining of bacteria is concerned. He should, however, be able to pre- 

 pare the more important stains, mordants, and other solutions which 

 may be required by the city or health board bacteriologist or the phy- 

 sician, and we shall therefore give the more commonly employed 

 preparations. 



A. Stock Solutions. — Make saturated solutions of the basic dyes (fuch- 

 sin, gentian violet, and methylene blue) in 95 per cent, alcohol. Keep 

 these in glass-stoppered bottles in a cool, dark place, ready for use in pre- 

 paring the stains. The stock solutions should in all instances be filtered 

 before using. Secure the dyes from reliable dealers and in small quantities . 

 Do not make up large quantities of stock solutions or stains proper, as 

 they gradually deteriorate, particularly if exposed to hght. 



B . Mordants. — The principal substances used are anihne, carbolic acid, 

 tannic acid, glacial acetic acid, ferrous sulphate, sodium hydroxide solu- 

 tion, chromic acid, and a few others. Those in general use are the two 

 first named. The others have a more limited use in special cases. 



Shake frequently, and finally filter several times through filter paper. 

 It should be perfectly clear. This preparation deteriorates rapidly. 

 Make up small amounts and keep in a dark place. It becomes worthless, 

 even when observing all precautions, in a few weeks. 



