26 A. W. GREELEY. 



or more and is at first of an exceedingly transitory nature. But 

 with paramoecia that have been reared in a culture that has 

 been made slightly acid by the fermentation of starch, and hence 

 are in an acid-modified condition as before described, the sec- 

 ondary reaction may begin as soon as the paramoecia reach the 

 cathode. In these cases no gathering occurs at the cathode but 

 each Paramaeciuin immediately reverses the stroke of the cilia 

 and swims back to the anode. The process is repeated at that 

 point, so that we have for a time no collection at either pole but 

 a continuous line of paramoecia swimming in either direction 

 until eventually they come to rest in about equal numbers at 

 each end of the preparation. Under the most favorable acid 

 conditions a number of paramcecia, varying from one to fifty per 

 cent, of the whole number, exhibit an initial reaction toward the 

 anode and a secondary reaction toward the cathode, while the 

 remainder react in the manner described above. 



That this immediate reversal of the normal reaction and the 

 initial response toward the anode are due to the acidity of the 

 culture medium may be shown by the following experiments. If 

 5 c.c., of a neutral 1 culture of paramcecia be isolated and tested 

 to the current, it will be found that they all exhibit the character- 

 istic response toward the cathode and form a dense gathering at 

 that point. If now, however, from two to four drops of an ml 10 

 solution of hydrochloric or other acid be added to the culture, 

 and, after standing for thirty minutes, the reaction to the current 

 be again tested, it will be found that either an initial or an imme- 

 diate secondary reaction toward the anode has set in. Also the 

 addition of a small amount of acid to an already acid culture 

 invariably strengthens the anodal response of paramcecia. Like- 

 wise in every case in which I have tried it, the neutralization of 

 the acid with NaOH, or the addition of the solution of a salt with 

 a trivalent anion like Na 3 PO 4 or Na 3 C ( ,H 5 O 7 entirely destroys 

 both the initial and the secondary response toward the anode, 

 and leaves only the characteristic gathering at the cathode. 2 



1 It is necessary to use paramcecia from an approximately neutral culture for this 

 experiment. The normal reaction toward the cathode is too firmly fixed in para- 

 mcecia from a strongly alkaline culture to be reversed. 



2 More striking results have been obtained with Vohox. After an exposure of half 

 an hour or more to a slightly acid medium, practically every organism completely 

 reverses its response, so that a dense gathering is formed about the anode. 



