mantle that extends iu irregular fashion beyond 

 the denser endoplasmic portion of the cell (figs. 

 125 and 143) . The hyaline mantle in the latter 

 figure is somewhat more lightly stained. In con- 

 trast to the mantle, the central reticulum retains 

 an approximately round shape. 



Weiss and Fawcett (1953) mention the ex- 

 istence of a mantle in avian monocytes when 

 grown in tissue culture. The mantle was found 

 to be visible when cells were examined under the 

 phase microscope. It is not altogether clear that 

 the type of mantle (thin undulating membrane) 

 they obsei-ved, and the type we have described 

 are identical. Weiss and Fawcett believed that 

 mantle formation is part of the process whereby 

 monocytes become macrophages. Additional 

 support for the idea that monocytes may become 

 macrophages comes from Dawson's (1933a) 

 study of blood cell reactions to lead poisoning in 

 Necturus. 



Since monocytes are large cells they are dis- 

 torted more readily during the process of making 

 dried smears than are small cells. The cyto- 

 some and even the nucleus often are squeezed be- 

 tween other cells, and so take various angular 

 shapes, or they may overlap other cells. These 

 variations occur most readily when there is a 

 hyaline mantle. If, however, they happen to fall 

 in an open space free from other cells, they 

 usually show a round contour and cells such as 

 these are the ones usually selected for drawing. 



Nuclear position. — The nucleus in many 

 monocytes is eccentrically placed, as may be seen 

 in figures 126-133 and 135; sometimes it forms 

 a bridge across the middle of the cell (figs. 134 

 and 136). The wide diversity of position is 

 shown in the outline drawings. In the first row 

 only 1 of 5 could be said to have the typical or 

 eccentric position. The proportion is about the 

 same in the other rows. The ratio of 1 eccentric 

 nucleus to 5 centrally placed is probably not a 

 true one because a dispropoi-tionate number of 

 cells selected for making the outline drawings 

 were atypical but were selected to show as wide 

 a range of morphologic expression as possible. 

 The eccentric position of the nucleus is of con- 

 siderable value in distinguishing between a mono- 

 cyte and a lymphocyte but it must be borne in 

 mind that a monocyte can have a centrally-placed 

 nucleus (fig. 151, A, b and B, a), as do many 

 lymphocytes. 



Nucleocytosomal ratio. — Not only are mono- 

 cytes larger than lymphocytes on the average but 

 the cytosome is proportionately larger than it is 

 in lymphocytes. This difference is not so great, 

 however, as superficial examination of cells might 

 lead one to believe. The eccentric position of 

 the nucleus gives the impression that there is a 

 large mass of cytoplasm; but when the same 

 quantity of cytoplasm is uniformly distributed 

 around a centrally placed nucleus there seems to 

 be only a narrow rim. This false impression is 

 magnified by the indentation of the monocyte nu- 

 cleus. The nucleocytosomal ratios for the two 

 cell types are given in table 4. They average 

 1: 0.47 for lymphocytes and 1:1.12 for mono- 

 cytes. In other words, the cytosomal area in 

 relation to nuclear area in monocytes is 58 per- 

 cent greater dian in lymphocytes. In terms of 

 nucleocell diameters the ratio is 1:1.22 for lym- 

 phocjrtes and 1 : 1.46 for monocytes. 



Cytoplasmic structure. — ^The descriptive term 

 "ground-glass effect" has been used by numerous 

 writers on avian blood. It is important to try to 

 understand what the structural elements are that 

 create the ground-glass illusion. Actually, we 

 have failed to see what others call the "ground- 

 glass effect." Any one of die following three 

 elements within the cell might be responsible for 

 the optical effect: 



(1) The open reticular framework such as 

 seen in figures 138 and 143, where there exist 

 numerous uniform spaces bounded by a delicate 

 reticulum. These spaces, however, have low re- 

 fractility; the term "ground-glass" suggests 

 rather conspicuous refractility. 



(2) The delicate orange-stained substance 

 that sometimes fills the vacuolar spaces in the 

 Hof (fig. 144). Figure 126 shows similar 

 spaces in the Hof but the material that fills them 

 has not taken an orange color. When the orange- 

 stained substance is present, it increases the con- 

 trast with the reticulum and thus gives the illusion 

 of greater refractility. This may be what has 

 been called the ground-glass appearance of the 

 monocyte cytoplasm. 



(3) The polychromatic reaction of the proto- 

 plasmic network (figs. 130 and 137) , which gives 

 a textural effect to the cytoplasm. The inter- 

 stices of the network that in the previous figures 

 took either a light or a dense basophilic stain 

 show in the last two cells mentioned a shift in 



68 



