TISSUE RECONSTRUCTION FROM DISSOCIATED CELLS 199 



become reconnected in aggregates, the cells rapidly established func- 

 tionally effective associations and became organized into tissues capable 

 of typical development ( Moscona and Moscona, 1952; Moscona, 1959a). 



This tendency of dispersed cells to reunite in vitro and to recon- 

 struct tissues raised a diversity of questions and possibilities. But pri- 

 marily it indicated that a proper application of this phenomenon un- 

 der adequately controlled conditions might, indeed, enable one to 

 compound cells into histogenetic fabrics and, by way of such experi- 

 mental synthesis of tissue, to examine some of the principles involved 

 in tissue formation and development. It also suggested that, by extend- 

 ing such studies to cells in different states and functions, normal and 

 pathological, to various physiological and environmental conditions, a 

 useful inventory of cell reactions could be obtained. 



The pursuit of these propositions in terms of precise tests hinged 

 upon the availability of an adequately controllable experimental frame- 

 work for such studies. For reasons referred to above, and others, self- 

 aggregation, while meeting the initial aims of this work, did not quite 

 fit the more rigorous requirements. For one thing, in depending on cell 

 movements upon the floor of the container it revolved around a cell 

 function, in itself highly variable and susceptible to extrinsic influences. 

 Furthermore, it involved relatively extended exposure of the individual 

 cells to the effects of the medium and of the floor-medium interface. It 

 is known that unless such exposure is brief, the cells do not remain un- 

 affected, and that various cell functions may become thereby markedly 

 and differentially modified (Moscona, 1959a; Holtzer, et al., 1960). 

 Consequently, the possibility arose that cell behavior in such self- 

 aggregating cultures, instead of representing predominantly first-order 

 reactions, reflected to a considerable extent intermedial, secondary re- 

 actions of complex nature and unknown causality. For precise study, 

 this was obviously not a very suitable situation. Therefore, one 

 needed a different cell-aggregation procedure, which would be based 

 on readily reproducible and controlled conditions and yield consistent 

 results in a manner suitable for precise assessment. 



Rotation-mediated aggregation 



To meet these requirements, an aggregation procedure was de- 

 veloped in which the initial amassing of the dispersed cells was not 

 dependent on their active movements (Moscona, 1961). The cells are 

 brought together by continuous, gentle rotation of the Erlenmeyer flasks 

 in which they are cultured. The swirling liquid forms a central vortex, 

 within which, under appropriate conditions, all cells accumulate rapidly 

 and, if capable of aggregation, become incorporated into loosely bound 

 masses ( see Figures 1-3 ) . 



