222 INFLAMMATION 



water. To reproduce partly these conditions a drop of clove 

 oil is placed in a mixture of glycerine and alcohol ; the alcohol 

 and clove oil are miscible, the glycerine merely retarding the 

 diffusion. 1 Such a drop of oil will move about, changing its 

 form and sending out pseudopodia much 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 pseudo- 

 podium. We can imagine that metabolic changes in the body 

 of an ameba may account for many of its seemingly 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. Amebse seem to 

 possess the faculty of selecting substances that are suitable for 

 their food, crawling over particles of sand, wood, etc., and reject- 

 ing them when they are pushed against or into the surface of 

 the ameba, which, however, readily takes up bacteria, diatoms, 

 algse, etc., digests them, and later throws out the undigested 

 particles. If there is any property of the ameba that suggests 

 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 amebse will take up many harmful 

 objects, and they may be made to fill themselves so full of use- 

 less 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 



1 The details of these experiments are as given briefly by Jennings, Jour, 

 of Applied Microscopy, 1902 (5), 1597. 



