V] THE FORM OF AMOEBA 211 



surface tension is greater, that portion of the surface will contract 

 into spherical or spheroidal forms ; where it is less the surface 

 will correspondingly extend. While generally speaking the surface 

 energy has a minimal value, it is not necessarily constant. It may 

 be diminished by a rise of temperature ; it may be altered by 

 contact with adjacent substances*, by the transport of constituent 

 materials from the interior to the surface, or again by actual 

 chemical and fermentative change. Within the cell, the surface 

 energies developed about its heterogeneous contents will constantly 

 vary as these contents are affected by chemical metabolism. As 

 the colloid materials are broken down and as the particles in 

 suspension are diminished in size the "free surface energy' 

 will be increased, but the osmotic energy will be diminished f. 

 Thus arise the various fluctuations of surface tension and the 

 various phenomena of amoeboid form and motion, which Biitschli 

 and others have reproduced or imitated by means of the fine 

 emulsions which constitute their "artificial amoebae." A multi- 

 tude of experiments shew how extraordinarily delicate is the 

 adjustment of the surface tension forces, and how sensitive they 

 are to the least change of temperature or chemical state. Thus, 

 on a plate which we have warmed at one side, a drop of alcohol 

 runs towards the warm area, a drop of oil away from it ; and a 

 drop of water on the glass plate exhibits lively movements when 



* Haycraft and Carlier pointed out {Proc. E.S.E. xv, pp. 220-224, 1888) that 

 the amoeboid movements of a white blood-corpuscle are only manifested when the 

 corpuscle is in contact with some soUd substance: while floating freely in the 

 plasma or serum of the blood, these corpuscles are spherical, that is to say they 

 are at rest and in equihbrium. The same fact has recently been recorded anew 

 by Ledingham (On Phagocytosis from an adsorptive point of view, Journ. of Hygiene, 

 xu, p. 324, 1912). On the emission of pseudopodia as brought about by changes 

 in surface tension, see also (int. al.) Jensen, Ueber den Geotropismus niederer 

 Organismen, Pflilger's Archiv, Liii, 1893. Jensen remarks that in OrbitoUtes, the 

 pseudopodia issuing through the pores of the shell first float freely, then as they 

 grow longer bend over tiU they touch the ground, whereupon they begin to display 

 amoeboid and streaming motions. Verworn indicates (Allg. Physiol. 189.5, p. 429), 

 and Davenport says {Experim. Morphology, ii, p. 376) that "this persistent cUnging 

 to the substratum is a ' thigmotropic ' reaction, and one which belongs clearly to 

 the category of 'response.'" (Cf. Piitter, Thigmotaxis bei Protisten, A. f. Physiol. 

 1900, Suppl. p. 247.) But it is not clear to my mind that to account for this 

 simple phenomenon we need invoke other factors than gravity and surface-action. 



t Cf. Pauli, Allgemeine physikalische Chemie d. Zellen u. Gewebe, in Asher-Spiro's 

 Ergebnisse der Physiologic, 1912; Przibram, Vitalitdt, 1913, p. 6. 



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