116 HISTOLOGY. 



form of the nucleus. They are somewhat smaller than the 

 large mononuclear cells, and are irregular in outline. Their 

 protoplasm varies in appearance according to the character of 

 the granules present (see below). The nucleus is absolutely 

 characteristic. With low powers it seems to be made up of 

 three or four small separate nuclei, which usually are arranged 

 in a semicircle at the edge of the cell. On examination with 

 higher powers, however, these nuclei are always seen to be 

 parts of one nucleus, and to be joined together by fine strands. 

 They stain very deeply in nuclear dyes, and can readily be 

 recognized in any tissue. These cells form about 62-70 per 

 cent, of the leucocytes in normal blood, and are found as wan- 

 dering cells everywhere in the body. They are found more or 

 less abundantly in all inflammatory processes, and are the main 

 cellular constituent of pus. They possess a special power of 

 taking up and either digesting or rendering innocuous bacteria 

 and foreign bodies in the tissues. This was studied specially 

 by Metchnikoff, and was called by him phagocytosis. 



The cells belonging to these four groups of leucocytes may 

 contain in their protoplasm various granulations, which have 

 been classified by Ehrlich according to their staining properties. 

 Ehrlich divides all anilin-dyes into three groups, namely: acid, 

 basic, and neutral dyes, according as the coloring principle is 

 an acid (as in ammonium picrate)*, a base (as in rosanilin ace- 

 tate), or a combination of a basic and an acid dye (as in rosani- 

 lin picrate). The most common acid stains are eosiri, orange G, 

 acid fuchsin, aurantia, etc., while the basic dyes ordinarily used 

 are methylene-blue, methyl-green, safranin, etc. Speaking gen- 

 erally, acid dyes color the protoplasm, and basic dyes the nuclei 

 of cells. 



Ehrlich distinguishes five different kinds of granulations, 

 and names them by the Greek letters a, /?, 7, 5, F. 



1. a (acidophile, eosinophile) granulations are usually coarse 

 and highly refractive, and are found mainly in polymorpho- 

 nuclear leucocytes. They stain brightly in eosin, aurantia, 

 indulin, nigrosin, orange G, etc. In normal human blood they 

 are found in very small numbers (0.25-4 per cent.), but in- 



