MORPHOLOGY OF LEUCOCYTES AND RED CORPUSCLES 223 



IV. Fixation by Formalin. — There are several methods by which 

 the fixative action of formalin can be used for blood-work. Of 

 these, the use of a mixture of i part of formaUn with 9 parts of 

 absolute alcohol answers perfectly. The films are immersed in 

 this for half a minute, and then washed thoroughly under the tap. 



This method of fixation is both good and rapid. 



Staining Blood-films for the Investigation 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. 



A cid 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. Ordinary basic fuchsin used in staining the tubercle 

 bacillus belongs to this group, as do hematoxylin, carmine, etc. 



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. Of these, the second 

 method is the simplest, and all that is necessary in the vast 

 majority of cases. The third method is an emergency one, for 

 use when Jenner's stain is not at hand : the first is now almost 

 obsolete, but occasionally useful when a study of the granulations 

 of the leucocytes is of importance. 



I. Ehrlich's stain consists of a mixture of acid fuchsin, orange 

 G, and methyl green dissolved in water, glycerin, and alcohol. 

 It is difficult to prepare, and should be purchased from a trust- 

 worthy maker. Its use is very simple. The film is fixed by 



