STRUCTURE OF PROTOPLASM OF PARAMCECIUM. 3 I 



line, the first form of reaction, characteristic of alkaline cultures, 

 returns, so that it becomes evident that the sense of the 

 chemotropic reaction depends direptly on certain chemical condi- 

 tions of the surrounding medium. The transformation from the 

 first form of reaction to the second, and vice versa, is a very 

 gradual one, so that it is not immediately effected by the chem- 

 ical change in the surrounding medium, and a considerable time 

 may elapse between the neutralization of the alkalinity of the 

 culture, for example, and the loss of the positive response to 

 alkalis ; but eventually the reaction occurs as has been described. 

 Thus paramcecia are seen to seek out those chemical conditions 

 which bring about a liquefaction of the protoplasm. The sense 

 of this response also is apparently determined by the electrical 

 condition of the protoplasm. 



An interpretation of the mechanism of this response to elec- 

 trolytes is as impossible as it was in the case of the reaction to 

 the electric current. But, since in each case the paramoecia col- 

 lect under the same electrical conditions, both responses must be 

 ultimately due to the same reaction of the contractile layer of 

 the protoplasm to electrically charged ions, and this reaction 

 must consist largely in the effect which the electrically charged 

 ions, have upon the surface tension of the contractile elements of 

 the protoplasm. Experiments upon Amoeba bear out this hy- 

 pothesis. Cathions always produce a contraction of the proto- 

 plasm, while anions produce a relaxation or the extension of 

 pseudopodia, because the former increase the surface tension of 

 the protoplasm while the latter neutralize it. Thus Amaba, 

 like Paramcecium, is positive to predominately negative solutions, 

 but in the one case the response is accomplished by the imme- 

 diate effect which the anions have upon the surface tension of 

 the protoplasm, while in the other case it is brought about 

 through the agency of a complex motor apparatus. 



CONCLUSIONS. 



We see that precisely those chemical changes in the surround- 

 ing medium, which modify the structural reactions of the proto- 

 plasm of Paramcecium to solutions of electrolytes, modify also 

 the reactions of the organism to electrical and chemical stimuli. 



