BLOOD-PLATELETS 23 



in the cancellated structure of the bones. They constitute about three 

 per cent of the total number of leucocytes. 



The third variety is called eosinophiles, on account of their affinity 

 for acid dyes, which strongly color the large granules contained in 

 their protoplasm. They also probably are derived from the red marrow 

 of the bones. They constitute one or two per cent of the total number 

 of leucocytes. 



In addition to the three varieties of leucocytes just described, a 

 fourth variety, called basophilic, is sometimes observed. These have 

 an affinity for basic aniline dyes. 



These four varieties of leucocytes probably by virtue of their 

 ameboid movements when they lie for a considerable time in contact 

 with the walls of the bloodvessels are capable of passing through 

 without solution of continuity in the vessels themselves. They thus 

 frequently pass out into inflammatory foci. They creep about in the 

 tissues and are then called migratory or wandering cells. 



Lymphocytes. The fifth variety is known under the name of 

 lymphocytes. They exist in the form of a rather small rounded 

 nucleus surrounded with clear cytoplasm. They constitute about 

 twenty-three per cent of the total number of white corpuscles. 



The five varieties of white corpuscles are produced chiefly in the 

 red marrow, but they also appear de novo in the substance of the 

 lymphadenoid tissues, the spleen, thymus and the lymphatic glands. 

 Treated with water or acetic acid, they swell and their nuclei become . 

 more prominent. They are dissolved in dilute alkalis. Although 

 they undoubtedly are developed in the red marrow, the spleen, thymus 

 and lymphatic glands situations in which the red corpuscles first 

 make their appearance the idea that they are finally developed into 

 red corpuscles, which at one time obtained, has been abandoned (see 



Plate I). 



BLOOD-PLATELETS 



In addition to the leucocytes, little homogeneous, ovoid, grayish, flat- 

 tened bodies TY ^o to Toioo of an inch 0-5 to 2 -5 A 1 ) in diameter, 

 have been observed and described under the name of blood-platelets 

 (Bizzozero). These bodies exist in the blood in the proportion of one 

 to about fifteen to twenty red disks, or 180,000 to 600,000 in a cubic 

 millimeter. Their origin is somewhat obscure, but it is thought that 

 their chief source is from the red corpuscles, which extrude a globular 

 matter having reactions like the nucleo-proteids. Their function is 

 equally obscure; but it is probable that they are concerned in some, 

 way in the production of prothrombin and are instrumental in bringing 

 about coagulation of the blood (see Plate II, Fig. i). 



