34 COMPARATIVE PHYSIOLOGY 



materials of the cell- wall. The disadvantage of surface tension 

 theories is that the results of microdissection studies reveal the 

 gelated character of the ectoplasmic membrane. In the 

 '' Umax " form the body of the organism is to be regarded, 

 according to Pantin, as a contracting tube of ectoplasmic gel 

 closed at its hind end. Endoplasm is continuously streaming 

 from a point of liquefaction on the inner side of the ectoplasm 

 at the tail end, while the fluid ectoplasm at the anterior extremity 

 is continuously adding to the contracting tube by becoming 

 gelated round the sides of the advancing pseudopodium. The 

 outer layer of the amoeba is apparently a lipoid-protein system 

 in the gel state, undergoing liquefaction, as Pantin 's observa- 

 tions indicate, in consequence of a local increase of hydrogen 

 ion concentration. Pantin argues that it is natural to regard 

 the swelling and liquefaction of the advancing tip of the 

 pseudopodium as a process of imbibition. By surface 

 coagulation the tube is always adding to itself in front, 

 and always contracting by synerezis (withdrav/al of water) 

 as the hydrogen ion concentration falls in the region furthest 

 behind. 



The variation of amoeboid activity with temperature is 

 seen in Fig. 12. The optimum temperature for the amoebae 

 which Pantin studied is remarkably low — about 20° C. The 

 effects of changes in temperature below 15® C. are completely 

 reversible. But when raised from a lower temperature to one 

 near the optimum or one above it, the previous rate is not 

 regained when the amoeba is brought back to a lower tempera- 

 ture. One of the factors upon which amoeboid activity depends 

 is therefore some substance or structural arrangement of 

 substances — probably an enzyme — which is progressively 

 destroyed near or above the optimum temperature. If the 

 temperature is raised from, say, 10° to T° (above the optimum) 

 and then rapidly lowered to 10°, the resulting velocity has a 

 precisely similar relation to the initial velocity at 10°, as has 

 the observed velocity at T° to the velocity that would have 

 been observed at T° if no destruction had taken place, since 

 the amount of destruction is identical in both cases. In this 

 way the observed temperature curve can be extrapolated 



