No. 453-] 



ACTIVITIES OF AMCEBA. 



the surface tension experiments; the direction of action of 

 the forces in these is evidently different from that in Amoeba. 



We may then turn to imitations of other activities of Amoeba. 

 Many attempts have been made to imitate certain of the reac- 

 tions to stimuli — particularly the positive reaction to chemicals. 

 Such imitations depend on the fact that a local decrease in the 

 surface tension of a drop of fluid may he caused by contact 

 with a chemical ; the drop then moves in the direction ot low- 

 ered tension. Some of the experiments based on this are the 

 following : 



Rhumbler ('99, p. 585) placed a small drop (60 to 90 /x in 

 diameter) of castor oil in alcohol, and brought close to it the 

 open end of a capillary tube containing clo\e oil, chlorotorm, or 

 5 ^ potassium hydroxide. The substance within the tube dif- 

 fused out against the drop of castor oil and decreased its surface 

 tension in the region of contact. Thereupon the usual currents 

 were produced (Fig. i), and the drop moved in the direction of 

 lowered tension, finally entering the tube. 



Bernstein (: 00) placed a drop of mercury in twenty per cent, 

 nitric acid, then brought near it a crystal of potassium l)ichro- 

 mate. By the chemical action the surface tension on the side of 

 the drop next to the crystal is decreased. Thereuixm the drop 

 moves rapidly over to the crystal, and ma\- i>ush ii al)oul from 



In the drops of clove oil in a mixture ol gl_\eernie and aK ohol, 

 described above (p. 8), similar movements may be .:iuse<l (Jen- 

 nings :02). With a cai)illary pii)ette a little aleohol 1-, bi ought 

 near one side of the drop, 'i'his decreases the surlaie tension 

 of the part affected; thereupon a projection is sent out toward 

 the alcohol, and the drop as a whole nwues towaid it. It the 



