more confident about the effect of charcoal. 



TS'O: I'd like to ask a question about the 

 data on aggregation. Is there a possibility that 

 some of the influencing substances are physical 

 in nature? 



KAHN: There's a very good possibility. 



POLLARD: Has anyone tried to prevent this 

 phenomenon in an electric field? 



KAHN: No, but I think it would be a very 

 good idea to check for possible bioelectric 

 phenomena in aggregation. In a single trial, we 

 were able to detect a potential difference be- 

 tween the front and back end of the slug. 



POLLARD: However, if this thing is alter- 

 nating very rapidly, perhaps you might not be 

 able to interfere with it. 



KAHN: The apparent rapidity of cell move- 

 ment in aggregation (note: as seen in a film 

 shown during this talk) is an illusion created 

 by showing time lapse photographs at normal 

 projection speeds. Actually cell movement is 

 quite slow. 



UNKNOWN DISCUSSANT: One last question 

 while we're on this subject of potential. Has 

 anyone tried the effect of chelating agents on 

 this phenomenon? 



KAHN: DeHaan did this with EDTA. 



UNKNOWN DISCUSSANT: Wouldn't this in- 

 terfere with the adhesion? 



KAHN: It does. Apparently the aggregates 

 formed without streams. That's why I think this 

 ought to be looked at in detail. 



GREGG: Gerisch also did this and he found 

 an EDTA sensitive stage and an EDTA insensi- 

 tive stage. After aggregation occurs, they're 

 EDTA insensitive so they stick together. 



UNKNOWN DISCUSSANT: Is there any 

 morphological polarity in these cells? 



KAHN: During aggregation, there is at least 

 transient morphological polarity. 



GREGG: Does your curve imply that founder 

 cells may occur as a result of aging of the cell? 



KAHN: "Developmental" age is probably 

 one of the factors that plays a role in the estab- 

 lishment of a founder cell. In this case, the 

 transition period between the end of feeding and 

 the onset of aggregation is probably the most 

 significant. 



EPEL: Is there any possibility they're 

 going anaerobic under mineral oil? 



KAHN: Mineral oil does permit the dif- 

 fusion of gases and you must bear in mind that 

 the layer used in these experiments was not 

 very thick. 



GREGG: Well, won' t they aggregate anaero- 

 bically anyway? 



B. WRIGHT: Yes, but what is called anaer- 

 obic sometimes is not strictly anaerobic. 



References 



1. G. Russell andJ. T.Bonner. Bull. Torr. Bot. 

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2. E.V/. Samuel. Develop. Biol. 3, 317(1961). 



3. B. M, Shaffer. In "Advances in Morpho- 

 genesis," M. Abercrombie and J. Brachet, 

 eds. (Academic Press, New York, 1962), 

 2, 109. 



4. J. T. Bonner and M.R.Dodd. Biol. Bull. 122, 

 13 (1962). 



5. J. T. Bonner and M. R. Dodd. Develop. 

 Biol. 5, 344 (1962). 



6. J. T. Bonner and M, E. Hoffman. J. Embryol. 

 Exptl. Morph. 11, 571 (1963). 



7. A. J. Kahn. Biol. Bull. 127, 85 (1964). 



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