6l8 V. T. NACHMIAS AND J. M. MARSHALL, JR. 



Mitchell: I should like to congratulate Dr. Marshall on a beautiful piece of 

 work. It makes one feel that the phrase "membrane transport" which we all keep 

 on using has a double meaning. We are speaking on the one hand of "membrane- 

 transport" and on the other hand of "transport membrane". Dr. Marshall has 

 just used the expression "transmembrane transport", and this is very descriptive 

 of what we usually mean by membrane transport (although we should more 

 logically say "transmembrane port"). The other kind of transport in which the 

 membrane itself is transporting and transported we ought, perhaps, to call "cis- 

 membrane transport " ! 



Holter: Just very briefly I would like to answer Dr. Allen's question from 

 before. While we have never seen in amoebae movements comparable with the 

 undulating movement that occurs in tissue culture cells, we have seen something 

 else that might be related to it and that is a peristaltic movement down along the 

 invagination of the amoeba surface. This peristaltic movement has been observed 

 in a time lapse film that Mrs. Chapman-Andresen made in Glasgow some years 

 ago. Unfortunately the film is technically not good enough to be published or 

 shown, but this special feature was rather distinct in several of the sequences. 



Allen : I would like to introduce one word of caution regarding the question 

 of the lability of the membrane in the amoeba. It may be quite true that under 

 special circumstances, such as during feeding and during pinocytosis, membrane 

 is indeed formed ; the fact that the cell can change from almost a sphere into a long 

 cylinder in a matter of a few minutes indicates that the cell can form a new mem- 

 brane. However, there is a vast amount of evidence in the literature showing that 

 during normal locomotion there is no membrane formed at the front end of an 

 amoeba. This evidence was gathered chiefly by Schaefl^er and by Mast. They 

 showed essentially that a particle placed on the surface of an amoeba, let us say 

 a quarter of the way back from the tip, remains in a constant position with regard 

 to the tip as an A. proteus type amoeba advances. However, if you watch particles 

 on the tail surface, their behaviour is not quite according to expectation, in terms 

 of the membrane being pulled forward on the surface of the amoeba. By and large, 

 it can be said that during normal locomotion there is no mass formation of 

 membrane. 



Holter : This fits very well with the fact that in amoebae pinocytosis and loco- 

 motion are antagonistic features. A amoeba that crawls will not pinocytose, and 

 vice versa. 



Marshall: I think there are many unsettled questions in this. But we are still 

 left with the finding that amoebae can rapidly form new binding material. We 

 don't know what is happening to the membrane proper, but at any rate there is 

 movement and renewal of the surface coat, and in a way it seems simpler to think 

 of membrane and coat as moving together. We have no direct evidence, so I will 

 have to leave it very open as to how this is done by the amoeba. 



Goldacre: With regard to the point made by Dr. Allen about the forward 

 motion of the membrane as indicated by carbon particles, I think there may be a 

 quite different interpretation of this motion, and that they are not strongly attached. 

 If one attaches a series of oil drops to the membrane, which can be seen to be 

 firmly attached because of their contact angle of 90, they do not move forward. 

 They are overtaken by the tail and are squeezed off eventually at the rear; so that I 



