70 HISTOLOGY 



was then stained with methylene blue, and mounted without being sec- 

 tioned. Most of it is colored pale blue, but the granules of the mast 

 cells are deep purple. Such granules, which assume a color different from 

 that of the stain employed, are called by Ehrlich metachromatic. The 

 granules of mast cells are so coarse that in favorable places, when examined 

 with an immersion lens, they can readily be counted. They spread over 

 and obscure the nucleus, which appears as a pale central area. 



Mast cells and eosinophiles were removed by Ehrlich from the miscel- 

 laneous group of plasma cells described by Waldeyer. Another type of 

 cell was discovered in syphilitic connective tissue by Cajal, and inde- 

 pendently described in tuberculous tissue by Unna (Monatsch. f. prakt. 

 DermatoL, 1891, vol. 12, pp. 296-317). He states that these cells (to 

 which the name plasma cells has come to be restricted) arise from normal 

 connective tissue cells by the increase and rounding off of the cell body. 

 As described by Unna, the granulation of the protoplasm is so fine that 

 even with the highest magnification the individual granules cannot be dis- 

 tinctly recognized as such. 



Typical plasma cells are shown in Fig. 56, p. They usually have 

 very round nuclei with characteristic coarse masses of deeply staining 

 chromatin. These masses may appear as wedge-shaped bodies with their 

 broad ends against the nuclear membrane so that they resemble the 

 spokes of a wheel ("Radkern") ; or the chromatin blocks may suggest 

 the squares of a checker-board. The nucleus occupies an eccentric posi- 

 tion in the mass of dense and deeply staining protoplasm. Specific granul- 

 ation, such as occurs in mast cells and eosinophiles, is absent. In certain 

 plasma cells, vacuoles are seen (Fig. 56, v) which contain a "homogeneous, 

 semifluid, colloid-like substance which has a strong affinity for acid dyes." 

 If the affinity for such dyes has become well marked, these vacuoles 

 form conspicuous structures, known as Russel's bodies. Usually they 

 are regarded as degenerative products, but some investigators consider 

 them as secretions. 



Associated with plasma cells, lymphocytes are often found (Fig. 56, 1). 

 These cells constitute an important class of white blood corpuscles or 

 leucocytes. They differ from plasma cells in having only a small rim 

 of pale protoplasm about the nucleus, but the nuclei of these two sorts of 

 cells are very similar. Although Ehrlich (1904) agreed with Unna that 

 only one source for the plasma cells had been established, "namely, an 

 origin from hypertrophied connective tissue cells," many authorities 

 now believe that they develop from lymphoid cells or lymphocytes. 

 Councilman expresses this opinion as follows (Journ. Exp. Med., 1898, 

 vol. 3, pp. 393-420): 



As to their origin I hold the same opinion as Marschalko, that they are derived from 

 lymphocytes. In the kidney they enter into the interstitial tissue by emigration from 



