l66 BACTERIOLOGICAL DIAGNOSIS. 



STAINING BLOOD FILMS FOR THE IN- 

 VESTIGATION OF THEIR CELLS. 



There are a great many methods of staining blood 

 films, and all depend upon the division of stains into 

 two varieties, the acid and the basic. All the stains 

 which are used in this branch of histology are salts ; 

 and in some of these salts the acid radicle does the 

 staining, in others the basic. 



Acid stains are those in which the colouring property 

 resides in the acid of the salt. A familiar example is 

 picrate of potash, a yellow stain in which the picric 

 acid is the active ingredient. The acid stains in chief 

 use are eosin, acidfuchsin, and orange G. Substances 

 which stain with an acid stain after suitable exposure 

 to a mixture of an acid and a basic stain are called 

 oxyphile, or, from the frequent use made of eosin as an 

 acid stain, eosinophile. 



Basic stains are those in which the colouring property 

 resides in the basic radicle of the salt ; they include all 

 the stains which are in use for staining bacteria and 

 they all colour the nuclei of cells. The most important 

 are methylene blue, methyl green, and toluidin. 



We shall describe three methods of staining, and 

 these are sufficient for all purposes of diagnosis. They 

 are: i. Ehrlich's method with his triacid stain; 2. 

 Jenner's method ; and, 3. Eosin and methylene used 

 separately. 



i. Ehrlich's stain consists of a mixture of acid 

 fuchsin, orange G, and methyl green dissolved in water, 

 glycerine, and alcohol. It is difficult to prepare and 

 should be purchased from a reliable maker. Its use is 



