THE BLOOD-CORPUSCLES 17 



seen to undergo slow changes of form. Processes called pseudo- 

 podia are pushed out at one portion of the surface, retracted at 

 another, and thus the corpuscle gradually moves or ' flows ' from 

 place to place, and envelopes or eats up substances, such as grains 

 of carmine, which come in its way. This kind of motion was first 

 observed in the amceba, and is therefore called amoeboid. It is 

 perhaps due to local alterations of surface tension; at any rate, 

 similar phenomena can be thus produced artificially. The leuco- 

 cytes of human blood are not all of the same size, and differ also in 

 other respects. They may be classified according to the presence 

 or absence of granules in their protoplasm, and the fineness or 

 coarseness of the granules ; according to the chemical nature of the 

 dyes with which the granules most readily stain, and according to 

 the form of the nucleus. Five or six varieties of leucocytes may 

 thus be distinguished in normal blood (Frontispiece) : 



1. Polymorphonuclear Neutrophile Cells. The nucleus assumes a 

 great variety of forms, often contorted or deeply lobed, the lobes being 

 united by fine strands of chromatin. The cytoplasm contains numerous 

 fine refractive granules, which stain best neither with simple acid dyes 

 like eosin nor with simple basic dyes like methylene blue, but with 

 mixtures which must be assumed to contain ' neutral ' stains, like 

 Ehrlich's so-called triacid stain.* These cells make up 65 to 75 per 

 cent, of the total number of leucocytes. Their diameter is 10 to 



12 /i. 



2. Eosinophile Cells (12 to 15 p in diameter), much less numerous in 

 normal blood than the neutrophiles (less than 5 per cent, of the whole), 

 but found in considerable numbers in the serous cavities, the connec- 

 tive tissue, and the bone-marrow. The granules in the cytoplasm are 

 coarser than the neutrophile granules, and stain much more deeply 

 with eosin. The nucleus may be simple, lobed, or even divided into 

 fragments between which no connection can be traced. It is less rich 

 in chromatin, and stains less easily with basic dyes, like methylene blue, 

 than the nucleus of the first variety. 



3. Large Mononuclear (also called Transitional) Leucocytes, with a 

 diameter of 12 to 15 /*. They possess a large simple or slightly lobed 

 nucleus, poor in chromatin, surrounded by a relatively great amount 

 of cytoplasm, with faint neutrophile granules i.e., granules which stain 

 with neutral dyes. They constitute 3 to 5 per cent, of the total number 

 of leucocytes. 



4. Lymphocytes of Two Varieties (a) Small Lymphocytes. Smaller 

 cells than any of the preceding (diameter 6 /*), possessing a single large 

 nucleus, surrounded by a comparatively small amoHnt of non-granular 

 cytoplasm; 20 to 25 per cent, of the leucocytes of the blood belong to 

 this group. The lymphocytes are markedly deficient in the power of 

 amoeboid motion in comparison with the other varieties of colourless 

 corpuscles. 



(6) Large Lymphocytes. The largest of all the white cells of the blood, 

 and at least twice as large as the small lymphocytes. They possess 

 a relatively great proportion of cytoplasm, which is devoid of granules. 

 They constitute no more than I per cent, of the total number of the 

 colourless corpuscles. 



* A mixture of orange G., acid fuchsin, and methyl green. 



2 



