222 THE BEHAVIOR OF LOWER ORGANISMS. 



There is much indirect evidence that points in the same direction, 

 particularly in the fact that the activities of the animal may remain con- 

 stant while the environment is continually changing. Some of these 

 lines of evidence are summarized by Rhumbler (1898, p. 185). They 

 still leave open the possibility that when the environment does modify 

 the movements its action is direct. But even this is shown to be 

 excluded by the nature of the currents produced, as described above. 



The currents as they actually occur in the movements are equally 

 opposed to certain theories of the indirect action of stimuli. Bernstein 

 (1900), Jensen (1901), and others, have expressed the opinion that the 

 effect of stimuli is to change the surface tension, but that this effect is 

 not due to the direct physical action of the agent on the protoplasm, 

 but rather to some change in the internal physiological processes of the 

 cell produced by the agent acting as a stimulus. Jensen (1901, 1902) 

 has developed this view into a detailed theory, according to which 

 stimuli that increase the normal assimilatory processes of the cell lead 

 to a reduction of surface tension, and hence to expansion and move- 

 ment toward the agent in question, while stimuli that increase the 

 dissimilatory processes have the opposite effect. 



The currents in the moving Amoeba lend no support to this view. 

 There is no evidence in the movement that the effect of a stimulus is to 

 alter the surface tension in any way. In view of the facts given in the 

 body of this paper as to the nature of the movements, we are forced to 

 give up the idea that the effect of stimuli is to modify the tension* of 

 the surface of the protoplasmic mass, either directly or indirectly. 

 Alterations in the tension of the surface can no longer be considered 

 the prime factor in the behavior of Amoeba. 



DIRECT OR INDIRECT ACTION IN THE TAKING OF FOOD. 



Rhumbler, in his most interesting and suggestive paper (1898), has 

 attempted to give a physical analysis of food-taking and the choice of 

 food in Amoeba. According to Rhumbler, the taking of food is due 

 to adhesion between the protoplasm and the food substance, and may 

 be compared with the pulling inward of a splinter of wood by a drop of 

 water, or of a bit of shellac by a drop of chloroform. The selection of 

 food is explained as due to the fact that the protoplasm, as might be 

 expected from physical considerations, tends to adhere to some sub- 

 stances and not to others. Parallel phenomena are shown, in a most 

 ingenious experiment, to be demonstrable for the chloroform drop 

 (/. c.i p. 248). It takes in certain substances, while others are refused 

 or thrown out if introduced. 



*See note, p. 225. 



