80 BLOOD 



a relation between these giant cells and the formation of blood 

 corpuscles. It seems probable, however, that these cells are more 

 concerned with degenerative processes, e. g., the absorption of the 

 nuclei of erythroblasts, than with the regeneration of blood cells. 

 THE BLOOD PLATELETS (third corpuscles, Uood plaques or 

 plates, hematoUasts of Hay em, tlirombocytes). The blood platelets 

 are minute ovoid or ellipsoid, colorless, granular bodies much 

 smaller than the red blood cells. They vary 

 considerably in size, but are mostly from 2 to 

 4/A in diameter. Blood platelets can be demon- 

 strated in living blood, and therefore form a 

 constant structural element of the blood. It is 



FIG. 82. A GROUP OF 



BLOOD PLATELETS, f ound that after drawing blood from the vessels 



FROM THE HUMAN these elements increase rapidly in number for 



a short period, and as their number is subject 



Veryhighlymagmfied. . . * . 



(After Eisen.) to constant variation from other causes it is 



impossible to assign them a definite numerical 



relationship to the red and white blood cells. The number of 



blood platelets has been variously estimated at from 200,000 to 



600,000 per cubic millimeter. 



The blood platelets present a remarkable tendency to collect 

 into masses containing considerable numbers of these elements. 

 It is in the vicinity of such accumulations that the first fibrils of 

 fibrin make their appearance during coagulation, and for this 

 reason the platelets have been assumed to bear an important rela- 

 tion to the production of fibrin in shed blood. 



Blood platelets as a rule present but little appearance of finer 

 cell structure. They are usually non-nucleated globular masses of 

 finely granular protoplasm which have a slight affinity for most 

 basic dyes and are deeply stained by gentian violet, thionin, etc. 

 Under favorable conditions they can be observed to execute amoe- 

 boid movements, sending out long and very slender protoplasmic 

 processes. Nuclei can also be demonstrated in at least a portion 

 of the platelets, and some observers (Deetjen,* Kopsch f) are in- 

 clined to consider them as being typically nucleated blood cells. 



The development of the platelets is still obscure. They were 

 formerly supposed, because of their basophile properties, to be 

 products of degeneration or of disintegration of the white blood 

 corpuscles. This theory has not received further corroboration. 



* Arch, f . path. Anat., 1901. f Anat. Anz., 1901. 



