FERGUS: I'm sorry; you left me. There 

 are bacteria present, and these cells can ingest 

 bacterial cells. 



B. WRIGHT: Yes, there are bacteria that 

 these cells like. 



FERGUS: All right, they're still there be- 

 cause you can get sorocarps with plentiful num- 

 bers of bacterial cells present. 



B. WRIGHT: Nol 



KAHN: No, I agree; you can'tl 



FERGUS: You certainly can; I've been able 

 to do it. 



B. WRIGHT: They're not the kind of bac- 

 teria that these cells like. 



DEERING: It's a question of whether 

 they're taking the bacteria up or not. 



FERGUS: Well, then there is some factor 

 that is controlling the failure of the amoebae 

 to ingest. 



DEERING: If you plate the myxamoebae out 

 on a lawn of bacteria, you can get colonies 

 of aggregation and culmination with bacteria 

 between the colonies. If you put only a few 

 amoebae down on a plate, they will divide and 

 then go to a final stage, but there will still be 

 bacteria that will be physically inaccessible to 

 them. You get clear regions in the bacterial 

 lawn that have been eaten out by the amoebae. 



GREGG: You can get aggregation among 

 bacteria; there's no question about that. Prob- 

 ably the differentiation mechanism overrides 

 the feeding one; you get aggregation in the 

 presence of bacteria, and they stop feeding at 

 that time. 



TS'O: Back to the original controversy. 

 Usually, I would think one of the chief purposes 

 of people working together in development is 

 trying to find the most important factor which 

 determines why a certain event will occur in a 

 certain way. On the other hand, some may think 

 that all factors involved are equally important. 

 It seems to me, therefore, there is a funda- 

 mental difference in philosophy and that's what 

 we are arguing about and what this workshop is 

 about. 



B. WRIGHT: It certainly is. It's a very 

 fundamental difference because people go looking 

 for the cause of morphogenesis when there are 

 many. 



TS'O: It's naive, but the systems we're 



working with clearly ask that question. 



B. WRIGHT: We have not picked small 

 enough problems to be able to find out wnether 

 it's naive or not. I mean, if you look at some 

 gross change, if you look at a sea urchin egg, 

 you know nothing about what's going on during 

 metabolism. Here in the slime mold, it's so 

 simpleminded that the main thing it's doing is 

 converting protein to carbohydrate, and you can 

 study a simple reaction in this process and 

 this has some meaning. If you attack a complex 

 system, you will not know what questions to ask, 

 or get around to knowing the answer to the ques- 

 tions, because you don't know enough about the 

 thing you' re studying. 



GROSS: But suppose, for the sake of argu- 

 ment, that somebody were interested in hemo- 

 globin synthesis. It's a very complicated sys- 

 tem. Suppose you're lucky enough to show that 

 at a certain time in the development of a chick, 

 for example, product x is to come off the shell. 

 This product becomes soluble and is a specific 

 inducer for the messengers that are involved in 

 the heme part of hemoglobin. Hemoglobin begins 

 to be synthesized and that, in turn, is responsible 

 for the aggregation or the differentiation of the 

 blood islands. 



B. WRIGHT: All right, you can make an 

 isolated observation like that and in this compli- 

 cated system that's as far as you'll go with it. 



TS'O: The question in my mind is whether 

 or not this organism has made an internal deci- 

 sion at this point to start differentiating or just 

 that it starts to differentiate when it has used up 

 its food. Look at all the synthesis of the cell 

 wall material. A tremendous amount of chemi- 

 cal energy is being used there. 



B. WRIGHT: There are many processes 

 begun when it starts starving at hours and at 

 15 hours it makes cell wall; if you look at what's 

 going on inside there, you see the proteins de- 

 creasing, the amino acid pool is diminishing, the 

 glucose is increasing, and the cell wall is being 

 made. 



KAHN: Pseudoplasmodia (slugs) can under 

 the appropriate conditions migrate for several 

 days. It is not until the slugs cease migrating 

 that final cytodifferentiation begins. Clearly, 

 the "cue" which triggers differentiation cannot 

 be "starvation" alone. 



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