38 



THE CIRCULATION OF THE BONE-MARROW. 



As stated in a preliminary communication (Doan, 1922), it is not until sections 

 as thin as 5 micra (fig. 2), from a relatively complete injection of a hypoplastic 

 marrow, are seen under an oil-immersion lens that the full import of the nature 

 and extent of the bone-marrow circulation begins to be realized and perhaps par- 

 tially understood. First of all, the gross structures the main longitudinal vessels, 

 transverse smaller branches, arterioles, a few transition capillaries, and the venous 

 sinusoids described above were easily verified in the serial sections. But in 

 addition to these I have found, appearing between the fat spaces in well-outlined 



Fig. 2. Drawing of a hypoplastic marrow, injected with india ink, showing venous sinusoid and intersinusoidal capillaries. 

 From the radius of an adult pigeon (19 A), e. c, endothelial cells lining capillaries, r. c, reticular cells of the 

 marrow; n. /. c, nuclei of fat-cells; r. b. c, red blood-cells; v. s., venous sinusoids; cap., intersinusoidal capil- 

 laries surrounding the fat-cells, with the granules of carbon of the injection fluid scattered throughout the 

 extent of their channels. These capillaries are seen to be in direct communication with the large venous 

 sinusoids via the characteristic conical openings. Hematoxylin and eosin; 5^X700. 



and clearly defined channels, a most extensive system of capillaries, hitherto 

 unsuspected. Many of these capillaries appeared to have been non-patent and 

 functionally dormant so far as the active blood circulation is concerned. This was 

 borne out by the difficulty and infrequency of their demonstration in the ordinary 

 marrow injections, where they were totally collapsed and could be seen only as 

 septa surrounding the fat-cell spaces. 



Figure 2 shows these extensively ramifying channels to be semi-collapsed. 

 Only a trace of fine ink-granules reveals the presence of a potential lumen, the 

 caliber of which appears insufficient for the passage of even a single blood-cell 

 without difficulty. Toward the epiphyses there is this complete encircling of each 



