118 A MANUAL OP BACTERIOLOGY 



may be used, fitted with pipettes, and several arranged in a 

 stand. " Drop bottles " are also convenient. 



Methylene-blue, Leishman and Giemsa preparations are more 

 permanent if kept unmounted. After examination with the oil- 

 immersion, the oil may be removed from the film with xylol. 

 Coles mounts these preparations in parolein. 



The best stains were Griibler's, but these are now almost un- 

 obtainable. Messrs. Burroughs, Wellcome & Co. supply many 

 anilin dyes and some other reagents, iodine, etc., in " soloids," 

 which are convenient and reliable. 



Grain's Method 



This is a method by which the organisms are stained, 

 but the ground substance, albuminoid material, tissue 

 cells and elements, etc., are decolorised and may be 

 counter-stained another colour, so that the organisms 

 stand out in marked contrast. It is particularly useful 

 for films of pus and other discharges, blood and tissue 

 sections. But only some organisms can be stained by the 

 process, so that organisms may be divided into those 

 that stain by it, Gram-positive, and those that do not, 

 Gram-negative, and the reaction is, therefore, also a means 

 of distinguishing various organisms. The method con- 

 sists in staining with a pararosanilin dye (e.g. gentian 

 violet, methyl violet, crystal violet, victoria blue, 

 thionine blue) in an anilin water or carbolic acid solution, 

 followed by treatment with an iodine solution. This 

 results in the formation of an iodine-pararosanilin-protein 

 compound within the organisms which is relatively 

 insoluble in alcohol, so that on subsequent treatment with 

 alcohol, the dye is removed more or less completely from 

 everything except the organisms (see also p. 133). Old 

 and degenerate organisms, even if Gram-positive, may 

 stain indifferently by the method, and some organisms 

 which in the tissues, blood or exudates are definitely 

 Gram-positive, under cultivation may become more or 



