THE CELL IN GENERAL. 31 



and the retina removed from the posterior half. If the 

 remaining portion, including the solera, choroid, and a 

 portion of the pigmented epithelium of the retina, be put 

 under water in a shallow dish, and brushed gently over 

 the surface with a fine camel's-hair pencil, delicate pig- 

 mented flakes will float off in the water. These are the 

 desired cells. One or two bits should be put into a drop 

 of glycerin on a slide. Another bit is put on to another 

 slide with a large drop of hsematoxylin solution, and after 

 about ten minutes the coloring fluid carefully washed off 

 with water, and the stained fragments placed with the 

 other in the glycerin on the other side. They are now 

 covered and examined. 



These cells appear hexagonal* and are joined together 

 edge to edge, giving a pavemented appearance to the frag- 

 ments. Most of the cell-bodies are closely crowded with 

 elongated brown or black pigment granules. Sometimes 

 such are seen as have but few granules within them, and 

 occasionally they are entirely free. When the cell-bodies 

 are crowded with pigment the nucleus appears as a round- 

 ed, indefinitely outlined structure, containing no pigment 

 and looking like a hole in the cell. When the pigment is 

 present in small quantity or entirely absent, the nucleus 

 is much less sharply outlined. In the cells which have 

 been stained with hsemotoxylin, however, the nuclei all 

 present well-defined outlines, and are stained of a violet 

 color. 



* These cells have really a very complicated structure, see page 244, 

 but it is not necessary to study this in detail here, since they are only 

 studied now for the purpose of demonstrating the occurrence of pig- 

 ment in the bodies of certain cells. 



