538 TRANSFORMATION OF ENERGY 



his views, are not quite correct ; he denies the existence of any close adhesion 

 of the advancing margin of Amoeba to the substratum, and shows that BER- 

 THOLD'S hypothesis necessitates internal currents in the plasma which must run 

 in the exactly opposite direction to that observed. For this and other reasons 

 BUTSCHLI holds that BERTHOLD'S theory cannot be accepted, and proceeds to 

 replace it with one of his own. According to BUTSCHLI amoeboid movement 

 resembles that seen in emulsions, as may be seen when one side of an oil drop 

 comes in contact with a soap solution. An oil-soap emulsion suitable for the 

 purpose may be obtained by triturating thick olive oil with potassium carbonate 

 and adding water to the mixture. The soap originally dissolved in the oil passes 

 rapidly into the water, which in turn diffuses into the oil, and the watery soap 

 solution dividesup into particles, giving the appearance of minute vacuoles in the 

 oily ground substance. According to BUTSCHLI'S observations, such a foam 

 shows a strong analogy to protoplasm, which also, according to this author, 

 generally, exhibits a frothy appearance (compare FISCHER, 1901). When 

 some of the vacuoles in such a foam burst unilaterally, the oil at that place 

 becomes covered over with a soap layer and the same conditions arise as when 

 a homogeneous oil drop surrounded by water is allowed to come in contact with 

 a soap solution on one side (Fig. 169). Under these circumstances, the drop as 

 a whole exhibits a progressive movement, and currents are set up in its interior 

 which recall very vividly those seen in Amoeba. 



The explanation given by BUTSCHLI of this phenomenon, cannot be dis- 

 cussed in detail here ; we will only note that, 

 in consequence of the lowering of the surface 

 tension at the point of contact with the soap, 

 a disturbance is set up in the equilibrium in 

 surface tension previously existing. One im- 

 portant point in BUTSCHLI'S explanation must 

 be drawn attention to, viz. that the strongest 

 currents occur immediately on the surface of 

 the oil drop (indicated by the larger arrows in 

 the figure), and that, owing to these, corre- 



Fig. ioq. Oil drop in contact with soap ,9 ' . , ,. 



solution. The arrows indicate currents, spending currents are set up in the surrounding 

 After BUTSCHLI (1892). water. BUTSCHLI has drawn our attention to 



another point in amoeboid movement, viz. that 



currents in that case in the water are absent or run in the opposite direction, 

 and he himself rightly concludes that his theory cannot be entirely correct in 

 all its details. 



From another point of view also important objections may be raised to the 

 foundation on which both BERTHOLD'S and BUTSCHLI'S theories are based ; these 

 we may just glance at, without mentioning the special difficulties which arise 

 in comparing the oily foam with protoplasm. PFEFFER (1890) has shown that 

 protoplasm enclosed in a cell-wall is generally in a liquid condition, but that in the 

 plasmodia of Myxomycetes a very obvious cohesion occurs in the passive external 

 layer. Stout strands of Chondrioderma may be subjected to a weight of 60 mg. 

 per sq. mm., but these strands recoil to their original length on removal of the 

 weight ; no permanent stretching takes place. Since, obviously, the external 

 passive layer has to withstand this pull practically by itself, PFEFFER calculated 

 that its tensile strength amounts to 300 mg. per sq. mm. When we remember 

 that, in order to tear asunder a lead filament of similar transverse area, a weight 

 of about 2 kg. is necessary, we see that the protoplasm of the Myxomycetes must be 

 a very delicate substance. All the same the cohesive force thus demonstrated 

 proves to us that we are not dealing with a genuine liquid. The cohesion in 

 the peripheral regions is further shown by PFEFFER' s (1890) observation that 

 vacuoles, when carried by the current through narrow channels in the plas- 

 modium, become deformed in consequence. 



