82 CARNEGIE INSTITUTION OF WASHINGTON. 



cell they break and discharge their granules into the surrounding medium. 

 In watching the phenomena accompanying death of a cell, it is interesting 

 to note that the ameba continues sending out pseudopodia after the nucleus 

 and cytoplasm stain with methylene blue, which reaction in the case of tissue- 

 culture cells we have regarded as evidence of cell death. For the ameba it 

 is evident that motion, and not the reaction of the organism to stain, must 

 be taken as the criterion of life. 



The methods of tissue-culture have been applied to tissues of fish embryos 

 by Dr. Pauline H. Dederer, who has found that they constitute a very favor- 

 able material for the study of living epithelial membranes. She has been 

 able to show that both mesenchyme and ectoderm cells grow out from the 

 explants in the form of membranes, the ectoderm spreading out as a thin 

 layer upon the under surface of the mesenchymal membrane. In fundulus, 

 however, the spreading activity of the ectoderm occurs only where it is in 

 contact with mesenchyme, whereas mesenchyme readily grows out alone. 

 The mesenchymal cells are actively ameboid and frequently exhibit character- 

 istic, large, thin, fan-like expansions, by means of which they adhere to the 

 cover-glass and to each other. The peculiarity in the growth of the ectoderm 

 in fundulus may prove to have some bearing on the problem of the adhesive 

 property of cells, which has been specially studied by Dr. Lewis. 



Serosal Cells and Clasmatocytes. 



For several years Dr. R. S. Cunningham has been conducting a series of 

 experimental studies upon the omentum. In previous reports I have men- 

 tioned his work on peritoneal absorption and the phagocytic activity of the 

 peritoneal mesothelium. More recently he has devoted his attention to the 

 characteristics and relationships existing between the three great groups of 

 cells which constitute the framework of the omentum — clasmatocytes, fibro- 

 blasts, and the serosal lining cells. An important step in advance has been 

 attained in his success in the differentiation of the mesothelial lining cell from 

 the clasmatocyte. He accomplished this by testing the reactions of serosal 

 cells lining the peritoneal and pleural cavities to various types of stimuli and 

 found that their reactions are entirety different from those of the clasmato- 

 cytes, the fundamental behavior of the former being adapted toward secre- 

 tion, while the latter is toward phagocytosis. The serosal cell may take up 

 particles of dye, it may detach itself and become free, but it does not become 

 a clasmatocyte. Dr. Cunningham shows that in reality it is more closely 

 allied to the fibroblast than it is to the clasmatocj^te. It can, however, be 

 differentiated from the fibroblast by the institution of mild irritations, under 

 which circumstances the two types of cells clearly differ, both in form and 

 the manner in which they store vital dyes. 



In another study. Dr. Cunningham has found that the mesothelial cells 

 from different areas of the peritoneal surface exhibit certain peculiarities in 

 the manner in which they store vital dyes, sufficient to classify them in groups, 

 although they all conform to a general type. The principal groups are: (1) 

 general serosal mesothelium covering intestine, body- wall, liver, and dia- 

 phragm; (2) mesothelium covering the omentum; (3) mesotheb'um covering 

 the spleen. The germinal epithelium covering the ovary was found to store 

 vital dyes in an especially characteristic manner. Each cell contained a 



