152 



H. F. PARKS 



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Fig. 1. Section through portion of hepatic sinusoid. Erythro- 

 cyte at bottom right. Hepatic cells at left and top. Lumen is 

 lined by a single sheet of cytoplasm resting on hepatic-cell 

 villi extending through perisinusoidal space. Phagocytosed 

 gold particles are seen in membrane-enclosed vacuoles. 

 Magnification 26,000. 



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Fig. 2. Section through wall of hepatic sinusoid. Erythrocyte 

 at right. Hepatic cell on left. Endothelium is in two layers. 

 Pseudopod-like processes seen in lumen and between endo- 

 thelial laminae. Magnification -^ 48,000. 



Trabecular cytoplasmic processes were recogniz- 

 able only in transverse section where they appeared 

 irregularly round, oval, triangular, etc. Some tra- 

 beculae were situated between sheets of cytoplasm 

 I'orming a bilaminar endothelial lining; others pro- 

 jected into the lumen as pseudopods, where some of 

 them lay close to the sinusoidal lining, as though bent 

 downstream by the moving blood (fig. 2). Among the 

 trabeculae located in the lumen, some were lying in 

 correspondingly-shaped grooves in larger masses of 

 endothelial cell cytoplasm so that they did not bulge 

 into the lumen, but presented one surface to it. In 

 some instances the surface depression that lodged a 

 trabecula was more than a groove; the lips of the 

 "groove" were not fused together, but came into 

 contact with one another above the trabecula, thus 

 forming a tunnel through which the trabecula passed. 

 Finally, many sections were seen in which a trabecula 

 was fitted into a canal surrounded by a continuous 

 wall of cytoplasm, the intercellular space appearing 

 as a closed circular cleft. It will be appreciated from 



this "piston-in-a-cylinder"" arrangement that endo- 

 thelial cells not only have elongate projections but 

 also form internal channels into which such projec- 

 tions can be fitted. 



Relation of endothelial cell to endothelial cell. — 

 This relationship is easily described for those areas 

 lined by thin sheets of cytoplasm. One process 

 merely overlapped another, and the intercellular 

 space apparently allowed blood plasma free access 

 to the perisinusoidal space, as was evident from the 

 fact that colloid particles passed between over- 

 lapping cells with ease (5). 



In the vicinity of the main cell body the rela- 

 tionship was sometimes more complicated, and is 

 not yet fully understood. In many cases the body 

 of one cell merely overlapped the attenuated cyto- 

 plasmic extension of another or a thin cytoplasmic 

 process of one cell was fitted into an appropriately 

 shaped recess in another. In some places, however, 

 two closely apposed (parallel) cell membranes ran 

 a complicated, sharply-curving course strongly 



