METABOLIC GRADIENTS IN AMOEBA 85 



the physical chemistry of contractility by observing and experi- 

 menting with amoeboid motion, its simplest expression. Rhumb- 

 ler has also conclusively shown the indefensibility of Dellinger's 

 point of view, in that amoeboid movement must be due to altera- 

 tions of the surface of some kind, for the simple reason that the 

 surface actually does change, this being the most obvious feature 

 of the amoeboid kind of movement. 



Another objection to the surface tension theory is that based 

 on the endoplasmic currents. These do not agree with the 

 currents produced in drops of fluid by local diminutions of the 

 surface tension. In such drops, the current flows forward in the 

 center towards the area of decreased tension, and away from it 

 in the entire surface. These currents are called 'fountain cur- 

 rents' by Rhumbler, and he thought the endoplasmic currents in 

 various Rhizopoda were identical with these fountain streams. 

 No one would presume to doubt the validity of Rhumbler's ob- 

 servations on the currents in Amoeba blattae, Pelomyxa, and 

 other forms as reported in his papers of '98 and '05, but the fact 

 remains that in most amoebae, and certainly in Amoeba proteus, 

 there is no backward flowing of the surface layer. This was first 

 pointed out by Jennings ('04) who remarks that Wallich had 

 noticed it in 1863, and Jennings has given a full discussion of the 

 matter to which I may refer without further comment. Del- 

 linger also notes the absence of any backward flowing of the 

 granules, and I myself must agree completely with the account 

 of Jennings (loc. cit., p. 135). In fact, according to the obser- 

 vations of Jennings, Dellinger, Gruber ('12), and Schaeffer ('16), 14 

 the surface of the ectoplasm actually flows forward at about the 

 same rate as the forward advance, and this indicates that the 

 advancing ectoplasm at the tip of the pseudopodium is derived 

 from the surface ectoplasm and not from a transform at ion of endo- 

 plasm into ectoplasm at the end of the pseudopodium as Rhumbler 

 supposed. Rhumbler in his discussion of Jennings' work 

 (Rhumbler, '05) says that the absence of the backward currents 

 is the result of the gelation of the surface, leading therefore to 



14 The forward movement of the surface layer of amoeba seems to have been 

 noticed first by Butschli ('94, p. 328). 



THE JOURNAL OF EXPERIMENTAL, ZOOLOGY, VOL. 24, ,NO. 1 



