ARTIFICIAL AMEB/E 269 



constantly undergoing chemical changes within itself, and taking sub- 

 stances from or secreting tliem into the surrouiuliiig water. To re- 

 produce partly these conditions a drop of clove oil is placed in a 

 mixture of glycerol and alcohol ; the alcohol and clove oil are miscible, 

 the glycerol merely retarding the diffusion.^" Such a drop of oil will 

 move about, changing its form and sending out pseudopotlia nmch as 

 an ameba does. These movements are undoubtedly due to changes 

 in the surface tension brought about by the irregular mixing of the 

 alcohol and the clove oil. The effect of chemotaxis upon an ameba 

 can likewise be imitated with such an "artificial ameba." If some 

 stronger alcohol is carefully introduced into the fluid near the drop, 

 the surface tension on that side will be lowered, and the drop will 

 flow in that direction. The effect of chemical changes within the drop 

 upon its motion may be demonstrated similarly by injecting a little 

 alcohol into the substance of the drop near one edge — the drop will 

 send out a pseudopodium on that side, and perhaps flow along in 

 the direction of the pseudopodium. AYe can imagine that metabolic 

 changes in the body of an ameba may account for many of its seem- 

 ingly purposeless movements by altering surface tension in some part 

 of its circumference. Thermotaxis, the effect of heat in modifying or 

 impelling ameboid motion, may be equally well demonstrated in such 

 an "artificial ameba," the drop being "positively thermotactic," and 

 flowing rapidly toward a heated point in the solution, because heat 

 lowers the surface tension. 



Even as highly specialized a process as the taking of food may be 

 closely simulated experimentally. Ameba' seem to possess the faculty 

 of selecting substances that are suitable for their food, crawling over 

 particles of sand, wood, etc., and rejecting them when they are pushed 

 against or into the surface of the ameba, which, however, readily takes 

 up bacteria, diatoms, algfe, etc., digests them, and later throws out the 

 undigested particles. If there is any property of the ameba that sug- 

 gests voluntary action, it seems to be exhibited in the choice of its 

 food, although this is not so well developed a selective process as 

 might be expected, for amebje will take up many harmful objects, and 

 they may be made to fill themselves so full of useless substances that 

 they cannot take up food. However, a drop of chloroform in water, 

 which makes a good artificial ameba, if "fed" with various substances, 

 will refuse some and take in others in a surprisingly life-like manner. 

 Pieces of glass or of wood placed in contact with the drop, exert no 

 influence ; if pushed into the substance of the drop, they carry the 

 surface ahead, and on being released they are throw^i out with some 

 force. If a piece of shellac, paraflln, styrax, or Canada balsam be 

 brought in contact with the surface of the drop, however, the drop 

 flows around it immediately, and takes it within its substance, where 



57 The details of these experiments are as given briefly hx Jennings. Jour, of 

 Applied Microscopy, 1902 (5), 1597. 



