3l THE BEHAVIOR OF LOWER ORGANISMS. 



described for Amoeba (p. 177, and Fig. 62, a). The chief experimental 

 difficulty in producing such bending is to arrange the conditions in 

 such a way that there is less soot on one side of a projection than on 

 the other. This occurs somewhat frequently when two irregular drops 

 are allowed to fuse, or when a drop is mechanically deformed with a 

 rod, as described in the next paragraph. One can sometimes bring it 

 about by placing with the capillary pipette a minute drop of oil on one 

 side of a projection, though this method is not as a rule very effective. 



Such drops may also show another prop- 

 >, erty in common with Amoeba, namely, 

 elasticity of form, or a phenomenon pro- 

 ducing similar results. Consider a curved 

 projection, as in Fig. 78, B. It is com- 

 pletely covered with soot particles and re- 

 tains its form in virtue of their resistance to a 

 change in position. Now, suppose we forcibly straighten out the pro- 

 section by pushing it to one side with a rod. By so doing the side a-b 

 is lengthened ; the soot particles on this side are, therefore, separated, 

 leaving certain areas of free fluid surface. When the projection is 

 released, surface tension can act on these areas, and the projection is 

 drawn back at once to its original form. I have often observed such 

 immediate returns to the original form after bending a projection of 

 one of the oil drops. 



In Amoeba we have exactly the conditions most favorable for the 

 production of movements of this sort, and we actually find numerous 

 movements of just this character. It is generally admitted that the 

 outer layer becomes partially solidified ; as a pseudopodium is with- 

 drawn the solid portions evidently become liquefied in an irregular 

 way, some of them projecting above the surface and making it rough. 

 If the liquid substance produced shows surface tension, the movements 

 described mustfollowin the manner set forth above. It seems possible 

 that many of the observed movements are thus produced by local lique- 

 faction, with the intervention of surface tension, in the liquefied area. 

 In view of the apparently unlimited possibilities of partial solidifica- 

 tion and liquefaction in the protoplasmic body, with the resulting varied 

 action of surface tension, shall we not go a step farther and inquire 

 whether there may not be an outlook for an explanation of vibratory 

 movements, such as we find in flagella, along this line? In an elon- 

 gated structure like a flagellum, a limited liquefaction of one side would 

 result in a bending toward this side. By regular alternation of lique- 

 factions in different regions, a regular vibration could be produced. 

 The chief difficulty in the way of such a theory would seem to lie in 



*Fio. 78. Diagrams illustrating phenomena in mixtures of oil and soot. 



