268 JXFLAMMATIOX, REGENERATION, OROWTH 



G. Quincke "^ later ascribed the contractions and other movements 

 of ameba? to alterations of the surface tension of the living substance 

 in relation to that of the surrounding medium, believing the sub- 

 stances responsible for the alterations to be albuminous soaps. 



Biitsehli ^* found that drops of "foam structure" made by mixing 

 rancid oil and potassium carbonate solution show '"protoplasmic 

 streaming" when placed in glycerol, and that they exhibit positive 

 chemotaxis toward soap solution and other chemicals, the motion be- 

 ing accompanied by current formation in the drops. The "pseudo- 

 podia" formed by the drops also show currents rushing along their 

 axes and returning by way of the surface. Heat leads to increased 

 activity of motion. The motions were ascribed by Biitschli to the 

 bui*sting of some of the superficial globules of the foam, which then 

 spread over the surface of the drops, lowering its surface tension at 

 the point of contact. He believed that ameboid motion, likewise, 

 depended upon rupture of surface globules of protoplasm, for the 

 "foam structure" of which he has been the leading advocate. 



Bernstein, ^^ basing his work on some observations of Paalzow, ob- 

 served that a completely inorganic substance, a drop of quicksilver, 

 could be made to imitate ameboid motion under the influence of 

 chemical changes. If a crystal of potassium dichromate is placed 

 near a drop of quicksilver in a nitric acid solution, as soon as the 

 yellow color made by diffusion of the dichromate reaches the drop the 

 quicksilver begins to show motion and advances toward the crystal. 

 This movement is due to local oxidation of the surface mercury, which 

 lowers the tension on that side of the drop, toward which the mercury 

 then flows. If the crystal is removed, the drop follows, often flow- 

 ing about it as if to take it in, but soon again withdrawing when the 

 acid dissolves away the oxide formed on the surface, only to return 

 again later. All these movements, which may be very life-like, are 

 readily explained by changes in surface tension that take place under 

 the influence of the bichromate and the acid, and are unquestionably 

 referable to surface phenomena. 



Artificial Amebae. — By far the most suggestive experiments on 

 the simulation of ameboid activity by non-living substances are those 

 of Rhumbler (1898) in his great work, " Pliysikalische Analj'se von 

 Lebenserscheinungen der Zelle. " ''^ On tlie assumption that the living 

 ])rotoplasm was but a more or less tenacious fluid, following the 

 simple pliysical laws of fluids, especially in relation to its surface ten- 

 sion, he devised a number of experiments to determine the correctness 

 of these viewg. An ameba may be regarded as such a mass of viscid 

 fluid, in a medium in wliich it is nearly or (|uite insoluble; it is also 



03 Wio<lniaiin"s Aiinalcii. ISSS (.35), oSO. 



54 "I'ldtojiliisiii." translation liy ^fincliin. T^ondon, 1804. 



55 Pfliifjer's Arcli., 1!)00 (80), 628. 



50 Arch. f. Entwic-klungsmechanik, 1808 (7), 103. 



