No. 3-] BLOOD-PLATES OF THE HUMAN BLOOD. 647 



Many groups of blood-plates are not surrounded by such a 

 plasma, and it can be seen that they adhere to each other 

 exclusively through their cytoplasmic projections. As regards 

 size, the blood-plates differ greatly from each other. Compared 

 with the red corpuscles of the blood, they are of course very 

 much smaller. In a general way it can be said that, taking the 

 groups of blood-plates as they are found, it takes from seven 

 to twenty plates to equal in size a red corpuscle, the varying 

 distance of the plates from each other being taken into account. 

 Some of the blood-plates are four or five diameters larger than 

 others. I have frequently found blood-plates the long diameter 

 of which equaled two-thirds the diameter of a red corpuscle. 

 Generally, however, they are much smaller, and I think it safe 

 to say that it takes about ten of the average size blood-plates to 

 equal a red corpuscle, the surface of the latter alone being 

 considered. Owing to the exceeding minuteness of the blood- 

 plates, their uncertain boundaries, and filamentous, cytoplasmic 

 projections, as well as to their variability in size, direct measure- 

 ments would be difficult to make and unreliable. 



VIII. Detailed Description of the Blood-Plates. 



Even a superficial examination of a blood-plate shows that it 

 consists of three distinct envelops or zones, one interior to the 

 other, and more or less concentrically arranged. 



A. In or near the center we find usually one, sometimes 

 two (seldom more), very bright, highly refractive globules, of 

 roundish, compact, irregular or regular form, and of a white or 

 yellowish color. They appear like a diamond in a dark setting. 

 These highly refractive globules do not stain. 



B. Surrounding these highly refractive bodies is seen a 

 darker area containing one or more dark granules, the latter 

 generally situated close together and connected by a dark- 

 staining film or irregular zone. 



C. Exterior to this is seen an outer, lighter-staining zone, 

 with many filamentous, cytoplasmic projections, by which the 

 blood-plates are made to adhere to each other and to other 

 objects in the blood. 



