814 PHYSIOLOGY 



(c) Those staining only with a mixture of the acid and basic dyes and 

 therefore spoken of as neutrophile. 



An acid dye is generally a salt in which the colouring-matter plays the part of an 

 acid radical. Thus eosin is the sodium salt of the coloured acid tetrabrom-fluorescein. 

 Basic dyes possess basic colour radicals. An example of this class, methylene blue, 

 is the chloride of the coloured base tetramethyldiphenthiazine. Neutral dyes, accord- 

 ing to Ehrlich, are those in which a colour base is combined with a colour acid, such as 

 the eosinate of methylene blue, or the picrate of rosaniline. 



In preparations stained with mixtures of these dyes we may distinguish 

 the following types : 



(1) The polymorphonuclear cells. These preesnt a lobed nucleus, and 

 their protoplasm contains abundant fine neutrophile granules. They form 

 about 70 per cent, of the total leucocytes. If the specimen be overstained 

 with eosin the granules may take on a red stain. 



(la) A few cells are sometimes seen with a horseshoe or hour-glass 

 nucleus and presenting a few neutrophile granules. These are spoken of 

 as transitional cells, and have been supposed to represent an intermediate 

 stage between large mononuclear or hyaline cells and the polymorpho- 

 nuclear leucocyte. They do not form more than 1 per cent, of the leuco- 

 cytes. 



(2) The lymphocytes are small cells with a round nucleus surrounded 

 by a thin layer of hyaline protoplasm which is free from granules. These 

 form 23 per cent, of the leucocytes. 



(3) Large mononuclear or hyaline corpuscles. These cells are two or 

 three times the size of a red corpuscle, and possess a large oval nucleus 

 which stains feebly with basic dyes. In normal blood not more than 2 per 

 cent, of the leucocytes are of this type. 



(4) In every well-stained blood-film the eosinophile corpuscle is very 

 evident, although not forming more than 3 per cent, of the white corpuscles. 

 The nucleus is generally single, but is often crescent-shaped or reniform. 

 The protoplasm is crammed with large discrete highly refractive granules 

 which stain deeply with eosin and give micro-chemical reactions for iron 

 as well as phosphorus. The granules, which in man, dog, and rabbit are 

 spherical, are cuboidal in the horse, and in birds have the shape of short 

 rods. 



(5) A cell which is found with difficulty, but is apparently a normal 

 constituent of human blood, is the basophile leucocyte. This, which is 

 somewhat smaller than the polymorphonuclear cell, has a lobed or tri-lobed 

 nucleus and presents a number of granules in its protoplasm which stain 

 deeply with basic dyes. It is sometimes spoken of as a ' Mast ' cell, the 

 German term for the cell being used without translation. It does not 

 form more than 0-5 per cent, of the total leucocytes of the blood. The 

 granules are practically invisible in fresh specimens, in this respect pre- 

 senting a contrast with the eosinophile granules. The leucocytes as a 

 whole undergo variations in number according to the physiological state 

 of the animal and are increased during digestion, specially of a protein 



