220 INFLAMMATION 



face tension of the two substances, and hence the surface tension of a 

 liquid may be raised or lowered by dissolving various substances in it. 



ARTIFICIAL IMITATIONS OF AMEBOID MOVEMENT 



Imagining a drop of fluid suspended in water let it be a 

 drop of protoplasm, or oil, or mercury ; the drop owes its ten- 

 dency to assume a spherical shape to the surface tension, which 

 is pulling the free surface toward the center and acting with 

 the same force on all sides. The result is that the drop is sur- 

 rounded by what amounts to an elastic, w r ell-stretched mem- 

 brane, similar to the condition of a thin rubber bag distended 

 with fluid. If at any point in the surface the tension is les- 

 sened, while elsewhere it remains the same, of necessity the 

 wall will bulge at this point, the contents will flow into the 

 new space so offered, and the rest of the wall will contract ; 

 hence the drop moves toward the point of lowered surface 

 tension. Conversely, if the tension is increased in one place, 

 the wall at this point will contract with greater force than else- 

 where, driving the contents toward the less resistant part of 

 the surface, and the drop will move away from the point of 

 increased tension. The resemblance of these changes of form 

 and the type of motion produced to ameboid movement, is 

 apparent, and much experimenting has been done to determine 

 how far the processes of motion as shown by amebse and leuco- 

 cytes can be reproduced by fluid drops under various conditions 

 of experiment, and to ascertain if such ameboid movement of 

 living cells can be entirely explained by the laws of surface 

 tension. 



Gad, 1 in 1878, pointed out the resemblance to ameboid motion 

 of the changes in shape observed in drops of rancid oils in 

 weak alkaline solution. These changes in shape are due to 

 the formation of soaps which lower the surface tension of the 

 drop in places, so that the fluid flows toward these places and 

 produces pseudopodium-like projections. 



G. Quincke 2 later ascribed the contractions and other move- 

 ments of ameba to alterations of the surface tension of the 

 living substance in relation to that of the surrounding medium, 

 believing the substances responsible for the alterations to be 

 albuminous soaps. 



Biitschli 3 found that drops of " foam structure " made by 

 mixing rancid oil and potassium carbonate solution show 

 "protoplasmic streaming " when placed in glycerine, and that 



'DuBois Keymond's Arch. f. Physiol., 1878, p. 181. 



2 Wiedmann's Annalen, 1888 (35), 580. 



3 " Protoplasm," translation by Minchin, London, 1894. 



