THE NUTRITIVE FLUIDS. 



1079 



of salt or sugar of the same specific gravity as the plasma, merely separates the 

 blood-corpuscles mechanically without changing their shape. 



The colorless corpuscles (leucocytes) are of various sizes, some no larger, others 

 even smaller, than the red corpuscles. In human blood, however, the majority 

 are rather larger than the red corpuscles, and measure about a fa to y^ of an 

 inch in diameter. On the average from 10,000 to 12,000 leucocytes are found in 

 each cubic millimetre of blood. 



They consist of minute masses of nucleated protoplasm, and exhibit several 

 varieties, which are differentiated from each other chiefly by the occurrence or non- 

 occurrence of granules in their protoplasm and 

 by the staining reactions of these granules when 

 present (Fig. 599). (1) The most numerous 

 and important are spherical in shape, and are 

 characterized by a nucleus, which often con- 

 sists of two or three parts (multipartite) con- 

 nected together by fine threads of chromatin. 

 The protoplasm is clear, and contains a number 

 of very fine granules, which stain with acid 

 dyes, as eosin (Fig. 599, 3). (2) A second 

 variety comprises about 2.4 per cent, of the 

 leucocytes ; they are larger than the previous 

 kind, and are made up of a coarsely granular 

 protoplasm, the granules being highly refrac- 

 tile and grouped round a single nucleus of 

 horseshoe shape (Fig. 599, 1). These granules 

 stain deeply with eosin, and the cells are 

 therefore often termed eosinophile corpuscles. 

 (3) A leucocyte characterized by the presence of a trilobed nucleus, and having 

 in its protoplasm fine granules which stain with basic dyes, such as methylene- 

 blue, is found in small numbers (Fig. 599, 5). (4) The fourth variety is called 

 the hyaline cell (Fig. 599. 4). This is usually about the same size as that of the 

 eosinophile cell, and, when at rest, is spherical in shape and contains a single 

 round or oval nucleus. The protoplasm is free from granules, but is not quite 

 transparent, having the appearance of ground glass. (5) The fifth kind of color- 

 less corpuscle is designated the lymphocyte (Fig. 599, 2), because it is identical 

 with the lymphoid cell derived from the lymphatic glands, the spleen, tonsil, and 

 thymus. It is the smallest of the leucocytes, and consists chiefly of a spheroidal 

 nucleus with very little surrounding protoplasm of a homogeneous nature ; it is 

 regarded as the immature form of the hyaline cell. The fourth and fifth varieties 

 together constitute from 20 to 30 per cent, of the colorless cells, but of these two 

 varieties the lymphocytes are by far the more numerous. 



The white corpuscles are very various in shape in living blood (Fig. 600), 

 because many of them have the power of constantly changing their form by pro- 

 truding finger-shaped or filamentous processes of their own substance, by which 



FIG. 599. Varieties of leucocytes found in 

 human blood. 1. Eosinophile cell with 

 coarse granules and horseshoe-shaped 

 nucleus. 2. Lymphocyte. 3. Polynuclear 

 or finely granular cell. 4. Hyaline cell, 

 showing nucleus with chromatin threads 

 and two centrosomes in clear protoplasm. 

 5. Finely granular leucocyte ; the nucleus 

 is lobed, the granules stain with basic dyes, 

 such as methylene-blue. 



FIG. 600. Human colorless blood-corpuscle, showing its successive changes of outline within ten minutes 

 when kept moist on a warm stage. (Schofield.) 



they move, and may take up granules from the surrounding medium. In locomo- 

 tion the corpuscle pushes out a process of its substance a pseudopodium, as it is 

 called and then shifts the rest of the body into it. In the same way when any 

 granule or particle comes in its way it wraps a pseudopodium round it, and then 

 withdrawing it, lodges the particle in its own substance. By means of these amoeboid 

 properties the cells have the power of wandering or emigrating from the blood- 



