CONNECTIVE 



1. Plasma Cells (Unna). These are cells of variable form, 

 whose protoplasm stains characteristically in polychrome methy- 

 lene-blue. They are found especially in the neighborhood of 

 small blood-vessels. Two varieties usually are recognized : 

 small plasma cells, which are similar in many ways to the 

 ordinary lymphocytes, and large plasma cells. According to 

 most authors, plasma cells arise from lymphocytes and later on 

 become fixed connective-tissue cells. 



FIG. 33. 



Blood- rensel 



Mast cell 



MtMGfffarU 



^Nucleus of 



""*- endothelium 



From the subcutaneous connective tissue of the rat. Along the vessel are found mast cells 



and two fat cells, x 540. 



2. Mast cells may assume all the forms of plasma cells. The 

 protoplasm is filled with round refractive granules which have a 

 special affinity for basic aniline dyes. The granules take a deeper 

 color than the rest of the tissue, and often assume quite a differ- 

 ent color (metachromatic staining). Dahlia-violet stains the 

 mast cells a characteristic reddish tint, while the other parts of 

 the tissue are colored only faintly. The nuclei, on the other 

 hand, take up stains only slightly, so that the nucleus-holding 

 portion of the cell appears pale (Fig. 33). The nucleus may 

 often be invisible if the darkly stained granules form a layer 

 covering it. The term " Mastzellen," which was proposed by 

 Ehrlich because, according to his idea, these cells appeared 

 under the influence of better nourishment, is somewhat inappro- 

 priate, for they are found often in senile and atrophic tissues. 



