BACTERIOLOGICAL TECHNIC. 7 1 



readily, thus intensifying the stain, as aniline oU and carbolic acid. Such 

 substances are called mordants, and may be used separately or added directly 

 to the stain itself. 



Certain liquids or solutions remove the stain from the bacterial cell 

 more or less readily, as water and alcohol, but more particularly solutions of 

 acids. Such substances are quite generally employed for removing any 

 excess of stain from the bacterial cell or from the matrix in which the bacteria 

 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 leproisy and of tuberculosis, while the great majority of species give up 

 the stain very readily. It is a fact 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 dearly 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 entire 

 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; in fact, even the 

 most skilled bacteriological technologists are apt to meet with small success, 

 and generally rest satisfied with the use of the single stain. 



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

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

 the more important stains, mordants, and other solutions which may be 

 required by the city or health board bacteriologist or the physician, 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 preparing 

 the stains. The stock solutions should in all intances 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 light. 



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

 tannic acid, glacial acetic acid, ferrous sulphate, sodium hydroxide solution, 

 chromic acid, andafew others. Those in general use are the two first named. 

 The others have a more limited use in special cases. 



