262 INFLAMMATION 



Artificial Amebae. — By far the most suggestive experiments on the simulation 

 of ameboid activity by non-living substances are those of Hhumbler (1898) in 

 his great work, "Physikalische Analyse von Lebenserscheinungen der Zelle."'* 

 On the assumption that the living protoplasm was but a more or less tenacious 

 fluid, following the simple physical laws of fluids, especially in relation to its sur- 

 face tension, he devised a number of experiments to determine the correctness of 

 these views. An ameba may be regarded as such a mass of viscid fluid, in a 

 medium in which it is nearlj^ or quite insoluble; it is also constantly undergoing 

 chemical changes within itself, and taking substances from or secreting them into 

 the surrounding water. To reproduce 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 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 direc- 

 tion. 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. We can imagine that metabolic 

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

 less 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 "posi- 

 tively 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 simu- 

 lated 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, alga^, 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 ameba; will take up many harmful objects, and they may be made to fill them- 

 selves 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 thrown out with some force. If a piece of shellac, 

 paraffin, 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 sub- 

 stance, where it is soon dissolved. Even more strikingly like phagocytosis and 

 intracellular digestion, however, is the result of a similar experiment with a piece 

 of glass covered with shellac; the chloroform "amel)a" takes it up as readily as it 

 does the shellac alone, but after all the coating is dissolved away the piece of glass 

 is then cast out of the drop. The resemblance to the engulfing, digestion, and 

 excreting of indigestil)le particles of bacteria, etc., by amel):r. is so striking that 

 it seems impossible that there can be any fundamental differences in the two 

 processes. It will al.so be noticed that the drop takes in only what it can dissolve 

 and rejects what it cannot. 



One of the most remarkable actions of the ameba\ which seems almost cer- 

 tainly the result of voluntary action, is this: Oftentimes in feeding, an ameba 

 gets hold of a suitable nuiterial which is in the form of a long tlucad, much too 

 long for the amel)a to surround. It then proceeds to coil up tlie (hreatl within its 

 body, by stretching a slight distance along the thread, bending over, and forming 

 a bend in the thread, and by repeating the i)rocess it crowds the tiiread into a 



'» Arch. f. Entwicklungsmechanik, 1898 (7), 103. 



"The details of these experiments are as given briellj' bv Jennings, Jour, of 

 Applied Microscopy, 1902 (5), 1597. 



