THE BLOOD. 



159 



graded ?) non-nucleated form mostly derived directly from the 

 former ; that in the first instance the blood-vessels and blood 



Fig. 144. 



(3(3(3(D 



Fig. 145. 



FiQ. 146. 



■' /"" — »\ Sum, 





7 



Fig. 147. 



Fig. 148. 



Fig. 144.— Cell elements of red marrow, a, large grannlar marrow cells; d, smaller, 

 more vesicnlar cells; c, free nuclei, or small lymphoid cells, some of which may 

 be even surrounded with a delicate rim of protoplasm; cf, nucleated red corpuscles 

 of the bone marrow. 



Fig. 146.— Nucleated red cells of marrow, illustrating mode of development into the 

 ordinary non-nucleated red corpuscles, a, common forma of the colored nucleated 

 cells of red marrow; 6, 1, 2, 3, gradual disappearance of the nucleus; c, large non- 

 nucleated red corpuscle resembling 2 and 3 of ft in all respects save in the absence 

 ' of any trace of nucleus. 



Fig. 146.— Nucleated red corpuscles, illustrating the migration of the nucleus from the 

 cell, a process not unfrequently seen in the red marrow. 



Flo. 147.— Blood of human embryo of four months, a, 1, 2, 3, 4, nucleated red corpus- 

 cles. In 4 the same granular disintegrated appearance of the nucleus as is noted 

 in marrow cells. 6, 1, microcyte; 2, megalocyte; 3, ordinary red corpuscle. 



Fig. 148.— From spleen. 1, blood-plaques, colorless and varying a little in size; 2, two 

 microcytes of a deep-red color; 3, two ordinary red corpuscles; 4, a solid, translu- 

 , cent, lymphoid cell or free nucleus. (Figs. 144-148 after Osier.) 



arise simultaneously in the mesoblastic embryonic tissue ; that 

 such an organ may exist after birth, either normally in some 

 mammals or under unusual functional need ; that the red mar- 

 row is the chief birthplace of colored cells in adult life ; that 



