214 HUMAN BIOLOGY 



phenomenon is observed when the food supply of fibroblasts 

 is modified. It is known that such cells growing from frag- 

 ments of adult connective tissue contain a small segregation 

 apparatus and a few slender mitochrondria. After they 

 have been fed well for a few days on embryonic proteins, the 

 segregation apparatus grows much larger and the nucleus 

 and mitochondria become similar to those of embryonic 

 fibroblasts. 



It is obvious that the anatomic constitution of a cell is 

 modified by its nutritional state. Cell morphology depends, 

 in some respects, on the nature and the concentration of the 

 substances which are free in the surrounding medium. 

 Moreover, the effect of the medium may be more radical 

 and lead to a transformation of the cell type itself. When blood 

 monocytes become crowded in a plasma coagulum, they 

 die or transform themselves into fibroblasts, that is, into a 

 type whose physiological properties are very different. 

 Secretory activity also depends on the nature of the peri- 

 cellular fluid. A pure culture of iris epithehum in embryonic 

 proteins gives rise to rapidly developing cells which contain 

 very few dark granulations. On the contrary, when the 

 rate of growth is decreased by the presence of blood serum, 

 a large amount of pigment is produced and the cultures 

 become almost entirely black. 



6. Effort toward Organization of Isolated Tissue Cells. 

 Tissue cells isolated from the body for several years retain 

 certain habits in the formation of colonies. They attempt 

 to join together by building up tissues of the same architec- 

 ture as were found within the parent organism. Fibroblasts 

 never scatter through the medium of the flask, but rather 

 pack themselves closely together in an intricate manner, 

 forming a felt-hke tissue which resembles young embryonic 

 tissue. Epithehal cells, on the other hand, practically 

 always unite by their edges and form a kind of pavement. 

 If fibroblasts are placed close to a pure culture of iris epithe- 

 lium, they quickly surround the epithehal cells which con- 

 gregate in acinus-like formation, as indeed Fischer has shown. 

 Although living far removed from the body in artificial 

 media, epithelial cells have a tendency to unite as they are 

 wont to do in the organism. A pure strain of Ehrlich car- 



