80 CARNEGIE INSTITUTION OF WASHINGTON. 



reached at 24 hours. Owing to the toxicity of the medium, few of these 

 cultures survived more than five days, as contrasted with normal cul- 

 tures, which live for two weeks or more. When diluted albumin was 

 used the phenomenon was retarded. When cultures were started in 

 Locke-Lewis solution and transferred to egg albumin, the al granules 

 did not appear for several hours, but after 20 hours these bodies were 

 about as abundant and as large as those in cells of cultures explanted 

 directly into egg albumin. In using the term "aV granules, Mrs. 

 Lewis does not mean to signify that they consist of albumin, but only 

 that they are the invariable result of the presence of albumin in the 

 environment of the cells. As for the factors concerned in the formation 

 of the al granules, Mrs. Lewis points out that there must be egg albu- 

 min in the medium in which the tissue is growing; a solution of peptone 

 will not suffice. Furthermore, it is evident that the phenomenon is 

 associated with conditions that are unfavorable to the life of the cell. 

 Whether it is a process of phagocytic nature or due to some change in 

 the cell membrane which permits the entrance of some material 

 normally excluded or prevents certain substances from passing out of 

 the cell, remains to be determined. 



Pigment-Producing and Pigment-Carrying Cells. 



Heretofore the pathologist has had no adequate criteria for deter- 

 mining whether, in a given pigmented cell, the pigment was formed 

 within it or had been ingested. The importance of obtaining some 

 means of distinguishing between the pigment-producing cell and pig- 

 ment-carrying cell will be appreciated when it is recalled that the 

 presence of the former in a new growth is an indication of a malignant 

 process, whereas the latter may mean nothing more than the phago- 

 cytosis of broken-down blood-elements. By means of tissue-culture 

 methods, Mr. David T. Smith has obtained criteria which apparently 

 enable one to accurately distinguish between these two varieties of 

 pigment granules. In the first place, he made careful observations on 

 the origin and development of melanin pigment in the retina of the 

 embryo chick, studied in vivo and in vitro. In cultures, the pigment 

 cells migrate out in the form of a thin membrane, thus offering an 

 excellent opportunity to observe the behavior of the cytoplasmic 

 granules in the living state. From such preparations it was found that 

 pigment granules are neither extrusions from the nucleus nor converted 

 mitochondria, as has been frequently maintained, but arise in the cyto- 

 plasm of the cell as small, colorless or gray granules, which appear at 

 about 42 hours' incubation. They gradually increase in size, number, 

 and depth of color until, at 17 days, the cell is filled with black rod- 

 shaped granules of uniform size. There is thus the stage of colorless 

 chromogen, followed by the stage of color production in the chromogen. 

 When formed, the pigment granules are very stable and are not de- 



