Observations on Early Stages of Phagocytosis 



155 



^ 1? 



B 



**• 





*? 



Fig. 1. Endothelial piiagocyte projecting into lumen of sinus- 

 oid. Numerous gold particles are adhering to its surface 

 15 seconds after intravenous injection. Two pseudopods are 

 seen in section at lower right. The endothelium on the oppo- 

 site side of the lumen is not entirely devoid of phagocytic 

 capacity: at A a particle has evidently been phagocytizcd, 

 and at B two particles are apparently in process of being 

 engulfed. Magnification 24,000. 





•^•r-^;"^'-- • ' A 



r.*.A. 



Fig. 2. Unusually potent phagocvte 2 minutes after injection 

 of colloidal gold. Lumen on right; perisinusoidal space on 

 left. One large branched cleft filled with gold particles is 

 seen communicating with lumen. At A a gold-containing 

 cleft communicates with the perisinusoidal space. At B a 

 rounded profile probably represents a spherical, membrane- 

 enclosed inclusion. Maunification 32,000. 



cause of their greater content of particles, many of 

 which were contained in spherical or spheroidal mem- 

 brane-enclosed inclusions of various sizes. In some 

 instances the membrane of an inclusion was seen 

 to be double. The most remarkable observation 

 made on this material was on certain particle-con- 

 taining cleft-like spaces (these may or may not have 

 been present in cells at 15 seconds following injec- 

 tion, but were not seen). These spaces ran a highly 

 irregular, sometimes branching, sometimes exagge- 

 ratedly serpentine course, suggesting that the section 

 was passing through an area of complicated inter- 

 digitation of two neighboring cells. However, in a 

 few instances a strong impression was gained that 

 the whole formation was intracellular; i.e., that the 

 cleft represented an extremely complicated infolding 

 of the surface membrane of a single ceil. Some clefts 

 that were obviously intracellular were seen appar- 

 ently breaking up into small spheroidal inclusions. 



some of which contained particles. Again, it was 

 impossible to decide whether such clefts, if intracellu- 

 lar, pre-existed or formed in response to the presence 

 of foreign particles. The small amount of particulate 

 material (often in widely separated groups) in some 

 clefts suggested that the clefts had not been formed 

 in response to the presence of the particles. 



It was further noted that a certain amount of 

 phagocytosis of material in the clefts passing from 

 lumen to perisinusoidal space had taken place, as 

 evidenced by spheroidal inclusions of particles in 

 the vicinity of these clefts. Also, some particles were 

 seen in clefts on the basal side of phagocytes, suggest- 

 ing that phagocytosis of material from the perisinu- 

 soidal space was taking place (tig. 2). 



In a morphological description of sinusoidal endo- 

 thelial cells (2) an intercellular relationship charac- 

 terized by a trabecular process of one cell passing 

 through a tunnel in another cell is described. The 



