DEPARTMENT OF EMBRYOLOGY. 71 



retina in the culture along with the growing spleen. Phagocytosis of the 

 granules was clearly not the result of any purposeful movement on the part 

 of the cell, but the result of chance contact. Furthermore, a certain extent 

 of surface contact was necessary, no melanin granule being taken in unless 

 it adhered to the cell throughout its entire length. The behavior of the 

 foreign substance after entering the cell was essentially the same as that 

 described by Dr. Smith, to which I referred in a previous report. 



From the reaction of the cells to vital dyes, Mr. Rioch concludes that 

 granules and vacuoles are not the result of a specific interaction of the dye 

 and the cell, because similar bodies appear in unstained preparations, while 

 in certain of the stained preparations no vacuoles or granules were observed 

 in either the lymphocytes or granulocytes. However, the number of granules 

 is increased in more concentrated solutions of the dye. Amceboid movement 

 of the blood-cells and macrophages can be easily observed under the con- 

 ditions attending Mr. Rioch's experiments, and he found that each type 

 exhibited its own characteristics. These he describes in detail. It is of 

 interest to add that in smears of the spleen he found very few endothelial cells 

 and obtained no outgrowth of them in the cultures. It would appear that 

 endothelium is not abundant in the spleen, since endothelial cells grow pro- 

 fusely in cultures from tissues in which these cells are present. 



Phagocytosis. 

 During the past few years considerable attention has been devoted in this 

 laboratory to the phenomenon of phagocytosis, as readers of our previous 

 reports will remember. Studies on living cells subjected to vital dyes, pig- 

 ment particles, and carbon particles have made it possible to determine 

 fairly well the physical nature of this phenomenon, and experiments on living 

 animals have shown the important role it plays in the absorption processes of 

 the body, both in health and disease. Dr. R. S. Cunningham has taken an 

 active part in these studies, and during the past year has made further 

 advances. He has shown that the chief means of transfer of granular material 

 from the peritoneal cavity into the diaphragmatic lymphatics is phagocytosis, 

 and this is accomphshed, not by free phagocytic cells, but by the mesothelial 

 lining of the diaphragm and the lymphatic endothehum. He proved this by 

 injecting particulate matter of various sizes (lampblack, carmine, erythrocj^es) 

 into the peritoneal cavities of young cats. The animals were killed at dif- 

 ferent intervals and the diaphragm and anterior mediastinal glands examined 

 histologically. Phagocytized particles were found in the glands after an 

 exposure of 5 or 10 minutes, and at the end of 30 minutes all of the lamp- 

 black and carmine had been phagocytized. Large numbers of granules could 

 be seen both in the diaphragmatic surface cells and in the lymphatic endo- 

 thehmn. An occasional red blood-cell had been taken within the cytoplasm 

 of the endothelimn. Careful examination of material exposed 30 minutes or 

 less failed to show the foreign matter being carried through by free phagocytic 

 cells, and there was no evidence that any of the material was passing between 

 the hning cells instead of through the cytoplasm. It is quite probable that 

 later on (after 30 minutes) leucocytes do bring into the capillaries many 

 granules, but it is also probable that the large inflow of free granules through 

 the phagocytic activity of the intervening cytoplasmic walls continues so long 

 as any remain free in the peritoneal cavity. 



