DEPARTMENT OF EMBRYOLOGY. 81 



stroyed by strong acids. They move about the cell with a character- 

 istic swift, jerky motion and remain discrete, showing no tendency to 

 clump together in vacuoles. 



Having ascertained the appearance and behavior of the granules of 

 the true pigment cell, Mr. Smith then studied the phenomenon of in- 

 gestion of pigment granules by the cells of various embryonic chick 

 tissues grown in Locke-Lewis solution. It was found that melanin 

 pigment obtained from the retina of the chick, pig, dog, and new-born 

 child is readily ingested in tissue-cultures of chick embryos by clasmat- 

 ocytes, fibroblasts, endothelial cells, white blood-cells, and cells from 

 the lung, liver, kidney, intestine, and amnion. On the other hand, it 

 is not ingested by the peripheral-nerve cells, striated-muscle cells, or 

 red blood-cells. When free in the culture fluid, the pigment granules, 

 in addition to progressing from place to place, exhibit a characteristic 

 Brownian movement; when attached to the cell-wall they become 

 motionless; after passing into the cytoplasm they exhibit the same 

 jerky motion noted in pigment granules in their native cells, until 

 finally a vacuole is developed about them, whereupon they revert to 

 Brownian motion. The manner in which the granules are ingested is 

 of interest. They are not engulfed by the throwing out of pseudo- 

 podia, as has been described for the amoeba. When the granule comes 

 in contact with the cell-wall, it is simply drawn into the interior 

 as if by capillary attraction, the result apparently of a local modifica- 

 tion of the cell-membrane. It is of interest also to note that the pig- 

 ment granule, on entering a cell, is not taken into a preformed vacuole, 

 nor does a vacuole immediately form about it; only after it has been 

 in the cytoplasm for some time is the vacuole formed. Once within 

 the vacuole the granule swells, breaks up into fragments, and is ulti- 

 mately reduced to minute particles of debris. It is the clumping 

 together of the granules into masses of irregular size and shape, their 

 inclosure in vacuoles, and their degeneration into debris that dis- 

 tinguish the ingested pigment from that contained in true pigment- 

 producing cells. 



The phenomenon of phagocytosis has also been studied by Dr. 

 G. B. Wislocki. Taking advantage of the fact that the endothehal 

 and reticular cells in bone-marrow tend to phagocytize and retain 

 soUd particles brought to them by the circulating blood. Dr. Wislocki 

 succeeded, by means of the thick deposit of pigment that can be thus 

 produced in the marrow, in demonstrating the distribution of the 

 marrow throughout the skeletons of new-born and adult rabbits, a 

 detailed description of which is given in his paper. His method con- 

 sisted of the injection of carbon particles (dilute india-ink) into the 

 blood-stream and a few days later sacrificing the animal, removing 

 the viscera, and rendering the remaining tissues of the body trans- 

 parent by the Spalteholz clearing method. After this procedure the 



