THE CIRCULATION OF THE BONE-MARROW. 39 



fat-space by these minute vessels. They are seen to lead directly from the large 

 venous sinusoids by way of typical conical openings and appear to be continuous 

 with them. This is illustrated in figure 3, which is an enlarged drawing of the 

 portion of figure 2 indicated by the square. These vessels are not capillaries, in 

 the sense of an arterio-venous transition, but extend from venous channel to 

 venous channel; they are intersinusoidal. There is no break in the continuity of 

 the endothelium which forms these slender channels from sinusoid to sinusoid. 

 There was no extravasation at any point and the material injected followed these 

 vessels everywhere. It was quite evident that these channels were closed, in the 

 sense that there was no extravasation or diffuse permeation of the tissues by the 

 injected ink. 



The attempt to differentiate an extravasation from a true circumscribed 

 distribution of perfused particles within definite channels was not made without 

 a full appreciation of the marked tendency of such granules to follow a reticular 

 framework closely in any injection into diffuse connective tissue. This character- 



Ink mass in sinusoidal vessel. 



Endothelial nucleus 



, , i ,, Fig. 3. A detail drawing of one of the typical conical open- 



Irwqranule in capillary . . *fj .... r . 



ings from a venous sinusoid into the semi- 

 collapsed lumen of an intersinusoidal capillary ; 

 indicated by insert in figure 2. 



nk mass. 



istic of reticular tissues to be outlined by extravasated particles, thus simulating, 

 more or less closely, definite channels, is recognized and acknowledged, and it is 

 obvious that the possibility of error of interpretation in injections of mesenchy- 

 matous tissue requires a corresponding amount of attention and care in analysis. 

 There were, however, five points apparent in the interpretation of these 

 studies which emphasize strongly the non-fenestrated character of the vascular 

 bed of the bone-marrow. (1) In injections showing a diffuse permeation of the 

 medullary parenchyma there have been demonstrable ruptures in vessel walls. 

 (2) In extravasation it was clear that the extruded granules were neither phago- 

 cytized nor regularly distributed along one side, but adhered promiscuously and 

 heterogeneously to the surface of the parenchymal cells, thus more or less concealing 

 their outline. In contrast to this, the particles within a definite lumen were 

 scattered here and there along the sides of the fining cells on the inside of the channel 

 only. (3) In an analysis of comparatively complete injections, showing this 

 extensive, inter-sinusoidal capillary bed, not only could these channels be distinctly 

 followed by the granules of ink, but the reticular network or framework of the 



