possiljle that an embryo carrying a pathogenic 

 organism could produce masses of reactive cells 

 that, after leaving their point of origin, become 

 thrombi of the circulating channels, but a simpler 

 explanation seems more reasonable at present. 

 When the glass cannula penetrated the ventricle, 

 it was quite likely, if the tip were dull or jagged, 

 tiiat some heart tissue, particularly the lining 

 cells, would he separated from the wall and would 

 then be sucked up with the blood. Hearts from 

 embryos of the same age — 10 days of incuba- 

 tion — were used in a test of this hypothesis. 

 They were removed from the body and opened, 

 and the l^lood was washed out. A slide was 

 pressed against the endothelial surface and from 

 it came the type of cells shown in figures 314^316. 

 Figure 316 was the longest cell obtained by this 

 method. Most of the cells were of the size and 

 shape shown in figure 314 and some were like 

 31.5. There is a measure of similarity of nu- 

 clear and cytoplasmic pattern between these cells 

 and those of figures 309 and 312. but there is still 

 room for douljt that they are all of the same type. 

 The endothelial cells of the liver and spleen are 

 phagocytic in pigeons (Kyes, 1915). The cells 

 are capaljle of ingesting erythrocytes under nor- 

 mal conditions and after the contained erythro- 

 cyte has been digested, the hemophage reverts to 

 a flattened endothelial cell. Kyes' observations 

 are mentioned here because it may help toward 



an understanding of the occurrence of macro- 

 phages within the heart of the embryo chick. 



It was noted, in the study of jjlood spots, that 

 macrophages underwent degeneration and only 

 some of the cells retained the punctate pattern of 

 chromatin of the type seen in figures 309, 310, 

 312, and 313. Often when karyolysis of the nu- 

 cleus occurred, the underlying nucleolus was 

 brought into view. There is a suggestion that nu- 

 cleoli are present in figure 312. Nucleoli were 

 conspicuous in some slides of chick embryos that 

 were sent to this Laboratory for cell identifica- 

 tion; the embryos had been inoculated with a 

 pathogen from man and the circulating blood 

 showed a series of transitional stages from the 

 reticular cell to the reactive cell. 



Some studies have been made on the defense- 

 reaction mechanism in lairds but perhaps the 

 greatest need at present is to identify by the smear 

 method the cells that, in the celloidin sectioned 

 material, are called resting amoeboid and wan- 

 dering cells. As the problem now stands, a 

 study of the actual number of different types of 

 macrophages is confused by differences in tech- 

 nics that make even identical cells look different. 



It has been claimed jjy Dantschakoff (1931) 

 that the endodermal wandering cell was actually 

 the primordial germ cell caught in its migra- 

 tion from the extraembryonic splanchnopleure 

 to the gonadal ridge. Dr. Robert E. Smolker of 



Figures 308-318. 



-Reticular or phagocytic cells found in blood and vascular organs of the embryo. 



2,470 X. 



308 Early embryo macrophage, yolk sac type. Blood 

 from dorsal aorta. Embryo incubated 1 day 22 

 hours. 



309 Embryo macrophage, beginning differentiation from 

 its stem cell. Circulating blood taken from the 

 heart. Embryo incubated 9 days 1 6 hours. 



Figures 310-313: Mature embryo macrophages and celt 

 fragments. Blood taken from the heart. Embryo incu- 

 bated 9 days 16 hours. 



310 Mature embryo macrophage. Only a few granular 

 inclusions. 



311 Cytoplasmic spheres ranging in size from large to 

 small, A to D. Believed to be pinched-off pieces of 

 macrophage cytosome. 



312 A group of macrophage stem cells, essentially 

 mesenchyme. Probably pushed into the cardiac 

 blood stream by the entrance of the cannula. Two 



nucleoli in each nucleus. Three embryo erythro- 

 cytes .shown in the field. 



313 Mature embryo macrophage containing acidophilic 

 and basophilic inclusions. Vacuolization typical of 

 functional macrophages. 



Figures 314-316: Cells from a touch preparation of imier 

 surface of embryo heart. They resemble, but may not be 

 identical with, those of figures 309 and 312. Embryo 

 incubated 9 days 22 hours. 



314 A nearly rounded cell. 



315 Cell with bipolar proce-sses. 



316 Cell with a long unipolar process. 



317 Postmortem degeneration of a macrophage, embryo 

 (21st day of incubation) killed and held in the cold 

 2 hours. Embryo still had a large external yolk sac. 

 Cell from spleen impression smear. 



318 Macrophage from blood of basilic (cubital) vein. 

 Chick just hatched. 



139 



