284 COLLOIDS IN BIOLOGY AND MEDICINE 



occurs; this may be induced for instance by an electric charge, 

 chemical reactions and the like. Thus a structure may retain its 

 general spherical form yet increase its surface at some single point, 

 flattening out, putting out limbs, pulsating, making slight movements 

 which may be explained purely by physical chemistry. The vital 

 phenomena of amebae and of leucocytes which are evidenced espe- 

 cially by movements of the plasma may be regarded as changes 

 in surface tension. Portions of plasma (pseudopodia) are far ex- 

 tended and the remainder of the body follows them, so that move- 

 ments of progression arise. Sometimes the pseudopodia surround 

 foreign bodies, a starch granule, a bacterium or the like and draw it 

 into the ameba or leucocyte; ingestion of food thus takes place. 



The migrations of an ameba, according to L. RHUMBLER, may be 

 deceptively imitated with a drop of chloroform in the following 

 way: A Petri dish is covered with an alcoholic solution of shellac 

 and the excess is poured off, so that after a few minutes the shellac 

 layer is superficially hardened. Boiled water is then poured into the 

 dish and a drop of chloroform dropped on the shellac with a pipette. 

 Immediately the drop begins its characteristic migration, especially 

 if it is pushed with a glass rod inserted between the chloroform and 

 the shellac layer. The phenomenon is explained as follows : a marked 

 surface tension develops between the chloroform, the water and the 

 moist shellac layer; soon chloroform and shellac commence to be 

 moistened at some point and at this point the surface tension of 

 the chloroform is lowered and it seeks to spread itself out. In this 

 way the chloroform drop progresses in a way similar to the flatten- 

 ing of the advancing margin of an ameba. The thin shellac layer 

 is dissolved by the chloroform flowing over it, so that the path 

 traversed by the drop " appears as if cut out of the shellac." Still 

 more deceptive is the similarity of movement if one does not take a 

 surface entirely covered with shellac, but prescribes the path of the 

 drop by a fine shellac line and retards the movements by the ad- 

 dition of Canada balsam or neat's-foot oil to the chloroform. Ac- 

 cording to the proportions of chloroform, size of drop, thickness of 

 the shellac layer and the degree of its dryness, the movements may 

 imitate the most diverse kinds of amebse. If a drop of chloroform 

 is placed on a spot of shellac which branches in various directions, 

 an imitation of the spreading of pseudopodia is obtained. The tak- 

 ing up of nourishment (taking up of oscillaria threads by ameba 

 verrucosa) may, according to L. RHUMBLER, be imitated when a drop 

 of chloroform in water comes into contact with a thread of shellac; 

 the drop completely envelops the thread of shellac and rolls it up 

 into itself. 



