No. I.] BLOOD CORPUSCLES. 



79 



which have been treated with a double stain of fuchsin and 

 methyl green the nuclei of the erythroblasts stain green, while 

 those of the leucoblasts stain red. Moreover, this method of 

 staining shows that the two kinds of cells are not intermixed 

 without order ; but on the contrary they are sharply separated, 

 the erythroblasts lying in cords or strings which are clearly 

 marked off from the masses of leucoblasts. These cords of ery- 

 throblasts form in reality a part of the vascular system of the 

 marrow in the following way. Between the well-defined arteries 

 and veins of the marrow there are two capillary plexuses. One, 

 a system of arterial capillaries comparatively few in number, is 

 connected with the larger arteries, and is composed of long, 

 narrow vessels with distinct, doubly-contoured walls. These 

 open suddenly into large venous capillaries which are nearly 

 filled with erythroblasts, and form, in fact, the cords of ery- 

 throblasts found in the marrow. The blood stream flows 

 through these imperfectly formed vessels in a central channel 

 which is more or less open, while the plasma probably percolates 

 through the whole mass of erythroblastic cells. These capil- 

 laries have a very delicate endothelial wall which marks them 

 off from the leucoblasts, and the erythroblasts filling them 

 are so arranged that the youngest lie next to the wall and 

 the most matured next to the central channel, where they can 

 be floated off by the blood current. The similarity of these 

 cords of erythroblasts or developing veins to the developing 

 veins found in the germ layers of the embryo by Wenckebach 

 (7) and Ziegler (8), and described and figured in the liver and 

 posterior limb of the embryo by me, will be apparent at once. 

 It would seem that the manner of development of the red 

 corpuscles is the same in the adult as in the foetus. Unfortu- 

 nately, Denys has not as yet shown that the same arrange- 

 ment is found in the marrow of the mammal, while others 

 positively state that no regular grouping of the blood-forming 

 cells occurs : so that this point remains to be investigated. 

 I shall have occasion to refer to it again. Feuerstack (17), it 

 will be remembered, held that in the birds and other animals 

 with nucleated red corpuscles the development of the corpus- 

 cles takes place in the blood-vessels of the marrow ; but he 

 gives no definite description of how this occurs. So, more 

 recently, Geelmuyden describes for the marrow of the frog 



