TISSUE RECONSTRUCTION FROM DISSOCIATED CELLS 



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Figure 9. Histogenesis in neural-retinal aggregates, a. A stained preparation 

 of cell suspension, b. A section through a 24-hour aggregate, c. A section 

 through a 56-hour aggregate, showing advanced differentiation of neural- 

 retinal tissue. 



cells capable of self-aggregating, or of being compounded by rotation 

 into coherent fabrics, but they promptly reconstruct replicas of their 

 original tissues ( Figure 10 ) . 



How is this structural and functional organization of the various 

 types of cells achieved within the aggregate? We have here cells which, 

 at the time of dissociation, were presumably already di£Ferentiated, i.e., 

 committed to a definitive set of activities. Do they retain, throughout 

 the events of dissociation and aggregation, their original identities and 

 functional commitments, or do they relapse into a more neutral, more 

 "flexible," state? Theoretically it is possible that the randomly bunched 

 cells in newly formed aggregates differentiate in accordance with their 

 chance locations within the re-established clusters; their development 

 in the new system might thus be a function of position. The opposite 

 possibility is that the eventual positions and functions of the cells are 

 dependent on and determined primarily by their original, pre-dissocia- 

 tion identities; this implies that the aggregated cells, though first as- 

 sociated at random, become rearranged and organized in accordance 

 with their native properties and functional kinships. 



Such alternatives might be adequately examined and resolved if 

 the cells were to differ sharply enough to be traced within aggregates 



