ACTIVE TRANSPORT AND MEMBRANE EXPANSION-CONTRACTION CYCLES 639 



follow cytoplasmic inclusions in the outer region of the ectoplasm as markers, you 

 find that they also accumulate over a two-minute period in the same tail region in 

 which the dye has been found to accumulate. Therefore, one expects that the 

 normal pattern in which cytoplasm circulates in the amoeba will cause dye 

 adsorbed to any part of the surface underneath the membrane to accumulate in the 

 tail. There is a second good reason why this accumulation should occur; if you 

 look carefully at the tail of an amoeba you find it contains a great deal of the surface 

 area. The membrane looks superficially like a bunch of grapes, or the surface of 

 large lobose villi. The greater surface area in the tail would lead one to expect 

 greater penetration of dye. A third factor which should be taken into account is 

 that when the dye penetrates, it enters small vacuoles which look very similar to 

 injury vacuoles. These form not only in amoeba but in other cells as well as a 

 result of neutral red treatment. Nowland in 1957 showed not only that neutral red 

 accumulates in vacuoles, but that the cytoplasm in the region of large accumula- 

 tions of neutral red vacuoles is in an injured state. Goldacre has once reported 

 finding an accumulation of stained particles which so altered the consistency of the 

 cytoplasm that they could be felt as a lump with a micromanipulator needle. If the 

 dye is sealed in vacuoles, it seems unlikely that it would tell very much about 

 molecular events in the ground cytoplasm. In view of these difficulties and 

 alternative interpretations of the dye accumulation phenomenon I believe that 

 one really can't draw any conclusions from it. I would also like to point out again 

 that Dr. Goldacre 's views on membrane formation and destruction just do not 

 conform with the results of many published experiments. 



Goldacre: I should like first to comment on the wrinkles in the amoeba's tail: 

 the area of membrane per unit mass of cytoplasm there would be several times that 

 in most other parts of the cell, but the amount of neutral red which accumulates 

 in the tail may be a hundred or a thousand times as much as you get elsewhere, 

 increasing as time goes on; so I don't think that passive diffusion through the 

 extra area of the wrinkles could account for the dye accumulation in the tail, by 

 several powers of ten. If it were a passive diffusion, as Dr. Allen suggests, the 

 amoeba would tend to become more uniformly coloured with time, say, after the 

 first few minutes; instead, the opposite occurs — the concentration in the tail 

 continues to mount, and the cytoplasm in the rest of the amoeba remains relatively 

 free of dye. 



With regard to Dr. Allen's statement that all the ectoplasmic particles accumu- 

 late in the tail region : that is not in accordance with my experience nor with the 

 published accounts of Mast and other careful observers; the particles circulate 

 indefinitely around the cell and do not accumulate anywhere. 



I don't think I can agree with Dr. Allen's third point because there are many 

 experiments which show that the membrane does not move forwards, including 

 those with oil drops which are attached to the membrane and when the contraction 

 of the tail advances up to them they are squeezed off" into the external medium; 

 carmine particles have indeed been shown to move forwards and I have seen that 

 myself, but I don't think they are properly attached to the membrane; you can 

 even see them moving forwards in the external medium separated by 10 or 20 

 microns from the surface of the cell, but with oil drops there is no doubt that the 

 attachment is firm, for the angle of contact is 90', I think the movement of carmine 



