30 A. W. GREELEV. 



ments, I find, that only those paramcecia which have been reared 

 in a slightly acid culture medium are positive to acids, and that 

 paramcecia from clear alkaline cultures are negative to acids and 

 positive to alkalis. It appears also that salts with trivalent 

 cathions act like acids, and salts with trivalent anions act like 

 alkalis. No definite conclusions could be drawn from the action 

 of the univalent and bivalent salt solutions. For the purpose of 

 the experiments, we are most vitally concerned with the reaction 

 of those solutions which carry the heaviest positive or negative 

 charges of electricity. 



The greatest caution is needed in determining the acidity or 

 alkalinity of the culture medium. A carefully prepared litmus 

 solution is the best indicator. Phenol-thalein may also be used 

 for the detection of small amounts of alkalis. Paramcecia freshly 

 reared in a culture whose alkalinity has been determined in this 

 way invariably react to the solutions used as follows : To ?;//2OO 

 HC1, HNO 3 , H 2 SO 4 , and acetic acid ; m/Soo A1 2 C1, ; and Fe 2 Cl c , 

 they are negative. To m / '200 NaOH, KOH, Ba(OH) 2 and 

 Sr(OH) 2 ; 1/1/480 Na 3 C 6 H.O 7 and Na 3 PO 4 , they are positive. 

 The positive reaction is shown by the organism swimming into 

 the drop, and then giving the motor response, described by Jen- 

 nings, when they come in contact with the outside water, so that 

 a gathering is formed within the drop. The solutions to which 

 the paramcecia are negative provoke the motor response when 

 the organisms first come in contact with the outer edge of the 

 drop, with the result that the solution is left empty. In some 

 cases the paramcecia appear to be entirely indifferent to a solu- 

 tion, and swim in and out in an undisturbed manner. Such a 

 reaction will also be classed as negative. 



If the paramcecia from the same alkaline culture be tested 

 from day to day as the alkalinity is being gradually neutralized 

 by the formation of acid during the fermentation of bread, or by 

 the addition of free acid to the culture, it will be seen that the 

 response to these solutions slowly changes, until finally the 

 chemotropic reaction is completely reversed, and now in the acid 

 medium the paramcecia are positive to acids and salts with a tri- 

 valent cathion, and negative to alkalis and salts with a trivalent 

 anion. Likewise, if the culture be again made gradually alka- 



