166 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, acid fuchsin, 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:—1i. Ehrlich’s method with his triacid stain; 2. 
Jenner’s method; and, 3. Eosin and methylene used 
separately. 
1. 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 
