556 ROBERT D. ALLEN 



the end of your capillary tube. What happens when you blow the material out of 

 your capillary tube on to a cover slip to form a circular drop ? Do you then find a 

 propagated contraction around the circle with no streaming ? 



Allen: In answer to your last question I think I would be restrained from 

 carrying out such an experiment as you suggest, by the fact that the cytoplasm of 

 the amoeba is so delicate that if one takes it out of the cell by anything but the most 

 careful methods, it fails to stream. In answer to your first question I am aware of 

 the ATP injection experiments which you reported in 1950, but I must remind 

 you that you didn't give very much information about the time relations in these 

 experiments or state the number of experiments that were performed. I should 

 think it quite possible that by poking an amoeba with a needle or a pipette you 

 might obtain almost any kind of behavioural result. I don't regard the changing 

 of direction of an amoeba in one experiment in response to ATP injection as proof 

 that phosphate energy from injected ATP has intervened in the contractile 

 mechanism. There are too many unknowns. The results you reported are certainly 

 compatible with this idea but it would take a great deal more data to prove it. 



GoLDACRE : Many repeated experiments showed an immediate contraction at 

 the site of injection of ATP. Injection of other substances (as we reported) had no 

 effect. Ts'o and his colleagues reported, in 1956, similar results to ours for the 

 microinjection of ATP into slime moulds ; they also demonstrated a reversible 

 lowering of viscosity of protein extracts from slime moulds each time that ATP 

 was added to the solution ; after the ATP was decomposed, the viscosity rose to 

 its original value ; this could be repeated indefinitely with the same protein solution, 

 just as with actomyosin. Loewy in 1952 also reported this effect of ATP on slime 

 mould extracts. 



Allen : But again it has to be demonstrated that the energy from ATP has been 

 utilized to stimulate the contractile mechanism ; ATP may have many more possible 

 effects than we now realize. The contraction you speak of is inferred from behaviour 

 rather than directlv observed. 



