CH. XI] 



STAINING MICROSCOPIC OBJECTS 



393 



appearance of differentiation even with a general stain, as the denser 

 portions of the tissue seem more deeply stained; that is, there is more 

 substance and more stain is taken up and hence the color is deeper. 



(2) From the standpoint of the solvent used in preparing the stains 

 they are called (a) aqueous, and (b) alcoholic. 



If one uses an aqueous stain the object must be well wet with water 

 before the stain is applied, and afterward well washed with water 

 before put again into alcohol. If an alcoholic stain 

 is used the object to be stained should be from 

 alcohol of the same strength as that used in mak- 

 ing the dye. The dye is also washed away from 

 the tissue with the same strength of alcohol; it 

 may then be put into the stronger alcohols for 

 dehydration. 



With reference to the now much used anilin 

 dyes, Wright, Principles of Microscopy, p. 34, 

 gives this excellent general statement: " Anilin 

 dyes may be regarded as salts containing a color- 

 ing element or chromophor, united to a base or 

 acid, according as the chromophor in question 

 possesses, in the particular case, acid or basic 

 properties. In the case where the chromophor 

 functions as an acid, the dye is denoted an acid 

 dye (e.g. eosin). In the case where the chromophor 

 functions as a base, the dye is designated a basic 

 dye." Eosin is used as an example where the 

 chromophor functions as an acid and methylene blue where the 

 chromophor functions as a base. 



The tissue elements, and their parts are named from their affinity 

 for acid or basic dyes. For example, in the blood, the red corpuscles 

 and the granules of some of the leucocytes have an affinity for acid 

 chromophores and hence stain strongly with eosin. They are accord- 

 ingly said to be acidophil or oxyphil, sometimes also eosinophil. The 

 nuclei of all the leucocytes, and of the red corpuscles when nucleated, 

 and the granules of some of the leucocytes, have an affinity for basic 

 dyes and hence stain with methylene blue, and are designated basophil. 



FIG. 234. REAGENT 

 BOTTLE WITH PI- 

 PETTE. 



