PLATE 2 
EXPLANATION OF FIGURES 
Bone-marrow 
33 A mesenchymal marrow cell, source from which hemoblasts develop. 
The cytoplasm is only very slightly basophilic, staining very faintly blue, and 
of homogeneous character. The nuclues is relatively large. It invariably con- 
tains a faintly staining plasmosome, occasionally several, and a number of larger 
karyosomes and innumerable minute chromioles scattered over a very delicate 
chromatic reticulum. The nucleus is vesicular in character and takes only a 
faintly blue stain. 
34 Primitive large lymphocyte (hemoblast). The nucleus is practically 
identical with that of its mesenchyme ancestor. It stains only slightly darker. 
The cytoplasm likewise seems more condensed and slightly more basophilic, of 
light blue color. 
35 Slightly older extravascular lymphocyte, in ameboid activity. The 
pseudopods may constrict off hyaline globules, similar to non-granular ‘platelets.’ 
36 Eosinophilic myelocyte; a slightly differentiated lymphocyte, with pseu- 
dopods forming hyaline ‘platelets.’ 
37 Medium-sized primitive lymphocyte (hemoblast); a slightly differentiated 
mesenchyme cell. Note the mesenchymal character of the nucleus. This cell 
may likewise develop into a granulocyte. 
38 Small extravascular primitive lymphocyte. 
39 Slightly later stage in the development of an extravascular small lympho- 
cyte, leading to a large lymphocyte or a granulocyte. 
40 Similar small lymphocyte with numerous pseudopods, which may form 
hyaline ‘platelets.’ 
41 Group of myelocytes from the periphery of a developing, small marrow 
blood-space. The cells include in order from above an erythrocyte, a poly- 
nuclear neutrophilic leucocyte, a large lymphocyte, an erythroblast, and a small 
lymphocyte. From the latter type of cell develop intravascularly both erythro- 
cytes and thrombocytes; from large lymphocytes develop intravascularly only 
neutrophilic granulocytes. From these large and small intravascular lympho- 
cytes develop also the various definitive lymphocytes of the circulating blood. 
42 A medullary erythrocyte (above) and a thrombocyte. (Compare with 
figs. 1 and 28 for demonstration of growth in passage from narrow to peripheral 
blood stream.) The cytoplasm of the thrombocyte varies in color from a very 
faint blue to a very light pink. It contains minute metachromatic (lilac) gran- 
ules of uniform size, grouped at the poles, and ranged apparently in single file 
along the lateral border. Thrombocytes apparently do not protrude pseudopods 
within the marrow. Their nucleus has in general the features of a small or 
medium-sized primitively mphocyte, from which cell the thrombocyte develops, 
but it is characteristically furrowed by deep oblique and longitudinal grooves. 
43 Similar medullary thrombocyte. 
44 to 50 Successive steps in the development of an eosiniphilic myelocyte 
from a primitive lymphocyte or hemoblast (compare figs. 50 and 11). 
(Continued on page 480) 
478 
