VITAL STAINING OF CORNEAL EPITHELIUM 43 



far as to say that the so-called 'Einschleppungstheorie' of melanin 

 is generally accepted, though the fact stated above shows the 

 possibility of its correctness. 



Though the observations here recorded have been made only 

 upon cells in culture, still it may not be impossible that the same 

 occurrence takes place in \dvo under certain conditions. At any 

 rate, the phagocytic action toward melanin of epithelium of the 

 adult frog in culture is here definitely shown. 



Therefore, it is not quite safe, in the culture of pigmented epi- 

 thehum, such as iris, to consider the pigment granules as the 

 peculiar possession of that epithelium, because the original non- 

 pigmented epithelium can ingest pigment granules. The study 

 of a complex and peculiar cell, such as the pigment cell, requires 

 great care in the methods used and in conclusions drawn. 



Carmin, which was gromid into fine powder, was also taken 

 up into the cell bodies, which then showed beautiful carmin 

 granulation. For this purpose the use of tissue, vitally stained 

 with Nile blue, offered great advantage. 



The arrangement and distribution of the granules was entirelj^ 

 similar to that of the melanin ; the particles were arranged with 

 considerable uniformity around the periphery of the cytoplasm. 



As figure 4 shows, corneal epithelium, cultivated in plasma (or 

 serum), containing both melanin and carmin, exhibits beautiful 

 melanin and carmin granulations which can be preserved safely. 

 Examination of such preparations in serial sections demon- 

 strated the intracellular and perinuclear position of the granules. 

 That they are in the cell bodies may be placed beyond doubt 

 even by the careful observance of fresh preparation. Further- 

 more, such preparations have the advantage of enabling the 

 observer to watch how cells with ingested granules may become 

 detached from the main mass and move off in the culture medium. 



Fine granules of Chinese ink or minute foreign bodies acci- 

 dentally mixed in the culture were also taken up by the 

 epithelium. 



In regard to this most interesting phenomenon of epithelial 

 phagocytosis, our present knowledge is very deficient. A strict 

 differentiation of the epithelial movement from that of leucocyte 



