No. 453-] 



ACTIVITIES OF AMCEBA. 



Rhumbler ('98) has given a physical imitation of the taking 

 in of a food body and of later giving off the undigested residue 

 (defecation). A rod of glass covered with a thin layer of shellac 

 is taken in by a drop of chloroform (as a result of adhesion). 

 The shellac is dissolved off by the chloroform and the glass rod 

 is then thrown out, since the chloroform does not adhere to it. 

 This imitation, Uke the others, loses much of its force in view 

 of the fact that food-taking is not usually due to adhesion and 

 that substances which do not adhere are taken as food ; defeca- 

 tion cannot then be explained as due simply to lack of adhesion. 



In all the imitations thus far we find that the physical factors 

 at work cannot be considered the same as those that are acting 

 in Amoeba. The imitations are such only in purely external 

 features. There exist certain imitations, however, in which this 

 has not been proved to be the case. Thus, Rhumbler ('98) 

 found that when chloroform drops are placed in water, the water 

 gradually passes into the chloroform, collecting in minute glob- 

 ules, which later gather in a larger drop. This larger drop is 

 finally given off to the outside. This process Rhumbler con- 

 siders analogous to the formation and discharge of the contractile 

 vacuole in Amoeba. The present author ( 104) has described 

 imitations of certain movements of the pseudopodia in Ama-ba, 

 produced in liquids partly covered with a solid layer ; these are 

 hardly of sufficient general interest to be detailed here. The 

 most striking experiments which can still be considered with 

 some degree of probability to indicate the factors really at work 

 in certain processes occurring in the Rhizopoda are undoubtedly 

 Rhumbler's imitations of the production of iJiHlugia shells. 

 Since these deal with an organi.sm closely related to Aino ba, 

 they may be described here. 



The experiments maybe performed as follows: Chloroform 

 is rubbed up with fragments of glass in a mortar until the glass 

 is reduced to the finest dust. Then with a pipette drawn out t<j 

 a small point drops of this mixture of chloroform and glass are 

 injected into water. At once the grains of glass come to the 

 surface of the drops so formed and arrange themselves in a 

 single layer, without chinks or crevices, exactly as in the shell 

 of Difflugia. The chloroform drop is thus covered with a shell 



