650 " EISEN. [Vol. XV. 



plasmocytes. The somosphere and centrosphere in the blood- 

 plates are less apparent, though in many instances (PI. XXXV, 

 Figs. 13, 16) I have satisfied myself of their identity. The 

 large, dark-staining, granulated area, which is always present 

 in the blood-plates, I do not hesitate to identify with the grano- 

 sphere of the plasmocytes of Batrackoscps. It is large enough 

 to be readily seen and recognized. The outer filiferous zone 

 of the blood-plates so greatly resembles the two outer zones of 

 the plasmocytes that their identity must be apparent even after 

 the most superficial examination. The filaments of the blood- 

 plates are longer than those of the plasmosphere of the plas- 

 mocytes, but their nature is otherwise the same. Through the 

 aid of these cytoplasmic projections, the plasmocytes as well as 

 the blood-plates adhere both to each other and to other objects 

 in the blood. On account of this great similarity in structure, 

 as well as in outward appearance and behavior, I do not hesitate 

 to say that the true blood-plates in the human blood are 

 plasmocytes, and, as such, must have the same origin as the 

 plasmocytes in the blood of Batrachoseps ; that they are really 

 composed of the centrosomes, with several cytoplasmic spheres 

 originally budded off from some nucleated red cells in the 

 human body, probably the erythroblasts in the bone marrow. 

 The process of separation has not been studied, but it is safe 

 to presume that it must, at least in a general way, be similar to 

 that observed in the blood of Batraclioseps (I. c, p. 18, etc.). 



X. Functions of the Blood-Plates or Plasmocytes. 



According to Bizzozero and others, the blood-plates in the 

 human blood, as well as the fusiform corpuscles in the blood of 

 the lower vertebrates, must be considered as being the direct 

 cause of coagulation of the blood. They are great, or perhaps 

 even exclusive, producers of fibrin. That the blood-plates act as 

 repairers of injuries to blood-vessels is now hardly ever denied by 

 investigators. The principal difference of opinion arises in the 

 question as to whether this function of the blood-plates is not also 

 shared by leucocytes and perhaps even by red blood-corpuscles. 

 To this controversy I cannot add any opinion based on ex- 



