a few small rings as is shown in figure 382, but 

 these are not like the large thin-walled rings 

 shown in figures 370-372. It was chiefly be- 

 cause of these characteristics that the decision 

 was made to place a cell found in the circulating 

 blood (fig. 193) among the basophils and not 

 among the heterophils. 



The question arises. At what stage of develop- 

 ment are the cells that are represented by figures 

 382 and 383? It is best that the magenta bodies 

 be ignored for the time being and that attention 

 be given to the nucleus and cytoplasm. The 

 cytoplasm of cell 382, slightly hypertrophied at 

 one side of the nucleus, is vacuolated and is be- 

 ginning to lose the strong basophilia of the granu- 

 loblast. If it did not have the magenta granules 

 it would be classed as an early metagranuloblast, 

 and figure 383 would be classed as a slightly 

 more dilferentiated cell at the same stage, but the 

 presence of the magenta bodies has been given 

 as characteristic of the promyelocyte. It is as if 

 two steps in development had been compressed 

 into one; therefore it is identified by reference 

 to its most conspicuous feature and is called a 

 promyelocyte — this is simpler than contriving a 

 new name to cover the two phases of development. 



This immediately raises the question. Are 

 these magenta bodies the specific granules charac- 

 teristic of basophils? If they are, these cells 

 should be called mesomyelocytes. At present 

 the opinion is held that these are not mature 

 specific granules and it is suggested that the defin- 

 itive basophilic granules of the more mature cell 

 develop out of the faintly stained substance of 

 the vacuoles. Thus, when the granules first ap- 

 pear, thev are the pale-magenta bodies shown in 

 figure 384 and from this pale staining condition, 

 by a progressive transformation, they produce 

 the dark-magenta bodies shown in figure 384 and 

 more abundantly in the three succeeding figures. 

 The nucleus of the basophil promyelocyte does 

 not lose its sharp boundary or the details of its 

 internal structure. This is because the cj^o- 

 plasmic vacuolization in the basophil is not so 

 vigorous as in the heterophil. 



On the right side of the nucleus of figure 382 

 is a bluish shadow that looks very much as if a 

 nucleolus were present below the surface. This 

 may be the case but in the granuloblast nucleus 

 it is not typical. (See addendvmi, p. 140.) 



Figures 384—386 are all mesomyelocytes, yet 

 each of tlie cells in the series is older than the 



one preceding. Cell 384 represents the first step 

 in the production of fully differentiated basophil 

 granules, and cells 385 and 386 show an in- 

 creasing number. By this method of fixation and 

 staining they appear to lie on a reticulum, but in 

 cells 388-390, which are fixed in methyl alcohol 

 and stained with thionin, no network joining the 

 granules is visible. It is probable that the net- 

 work is an artifact and the idea of differentiation 

 of granules from vacuolar substance was stated 

 only as an opinion because it is obvious that in 

 the bone marrow, as well as in the circulating 

 blood, aqueous solutions tend to dissolve and 

 distort the basophil granules. The nucleus also 

 seems to be adversely affected by the technic 

 treatment (figs. 385-387). Figure 387 is a late 

 metamyelocyte. 



There is need for additional search for a tech- 

 nic that will preserve the basophil granules and 

 still reveal the detailed structure of the cell. 

 Methyl alcohol and thionin preserve the granules, 

 but nucleus and cytoplasm stain alike and have 

 such a delicate blue color that no structural de- 

 tails are visible; so when it is stated in the legend 

 that figure 388 is a mesomyelocyte, figure 389 a 

 metamyelocyte, and figure 390 a mature baso- 

 phil granulocyte, this is based only on the num- 

 ber of granules present. 



PLASMA CELLS 



Plasma cells may be found in spleen and 

 bone marrow but are not common in normal 

 healthy chickens. A few examples from bone 

 marrow have been seen and are presented here, 

 and some that were observed in the spleen are 

 illustrated in figure 331, but in no case has a 

 cell been found that could qualify structurally 

 as a plasmablast. The possibility that such a 

 cell might be the primordial osteogenic cell in 

 bone marrow or the reticular cell in the spleen is 

 a reasonable assumption since the early imma- 

 ture plasmacyte (fig. 331, 1) resembles these 

 primordial cells. Mjassojedoff (1926) found 

 numerous plasma cells in the loose connective 

 tissue of adult chickens. He considered this 

 abundance to represent a point of difference from 

 mammals where they are said to be scarce. 



Figure 391 represents the earliest stage that 

 has been found. The cytoplasm form a much 



197 



