No. I.] GIANT CELLS OF THE MARROW. 



developing blood cells. This view was su-csted to mc by a 

 curious phenomenon which I have occasionally found in con- 

 nection with these giant cells, and which, so far as I know has 

 not been noticed before. In many sections of the marrow', but 

 especially in sections through the bone and marrow of the 

 femur of a foetal cat (9 cm. long), I have seen the megakary- 

 ocytes, either singly or in groups, with a delicate reticulum 

 radiating out from them on all sides, and enclosing within its 

 meshes the other elements of the marrow. A sketch of this 

 appearance is given in Fig. 7. I should add that Werner has 

 described but not figured what appears to be the same reticu- 

 lum. In the young developing marrow this appearance is so 

 common and so striking that I thought at first the megakary- 

 ocytes had for their function the formation of a supporting 

 reticulum for the marrow, secreting it, as it were, from the 

 cell substance. But when examinations were made of teased 

 specimens of the fresh marrow of young kittens to find if pos- 

 sible whether a giant cell with its reticulum could be teased 

 out from the other elements, I obtained the cells, surrounded 

 not by a reticulum, but by a very large envelope of exceedincrly 

 fine and pale material (Fig. 8). Round the nucleus of tlie 

 cell was the ordinary granular protoplasm forming the body of 

 the cell, but outside of and surrounding this was a large enve- 

 lope of much more delicate and hyaline material, which did 

 not stain with methyl green. As this was watched under the 

 microscope, in a very dilute NaCl solution of methyl o-reen vac- 

 uoles began to form in it (Fig. 9), and becoming rapidly laro-er 

 finally made a reticulum such as I had found in my sections 

 surrounding the cell. This convinced me that the reticulum 

 seen m the sections arose from the action of the fixing and 

 hardening reagents upon this secretion from the cell * The 

 theory that the giant cells make a reticulum is rendered im- 

 probable, also, from the fact that they occur in the developino- 

 blood-vessels of the embryo. In many cases in the teased 

 specimens the action of the reagent had gone so far that the 

 giant cells were found surrounded only by vesicular-like bodies 

 arising from the vacuolation of the secreted material, as shown 

 in Fig. 10. It seems to me that this broad envelope of mate- 

 rial surrounding the megakaryocyte, and evidently formed by it 

 IS very significant. As I found it, no nuclei were scattered 



