HURWITZ. — THE REACTIONS OF EARTHWORMS TO ACIDS. 79 



a sour taste about four times as 

 strong as it would be expected 

 to have, assuming that the taste 

 is due simply to the hydrogen 

 ions momentarily present. Kich- 

 ards obtained a similar result, in 

 that he found that the acetic acid 

 was about one-third as sour as 

 an equivalent solution of hydro- 

 chloric acid, though the acetic 

 acid was only dissociated to the 

 extent of one-fourteenth as much 

 as the hydrochloric acid was. 



To determine whether this dis- 

 crepancy existed also for the 

 earthworm, the following test was 

 made. Two solutions were pre- 

 pared, an 4^^ solution of acetic 

 acid and a weaker solution of 

 hydrochloric acid. Both solu- 

 tions, however, contained equiv- 

 alent numbers of hydrogen ions. 

 Worms were now tested in these 

 two solutions and the results are 

 recorded in Tables XVIII and 

 XIX. 



It is clear from these tables 

 that the earthworm, like man, is 

 stimulated by acetic acid more 

 vigorously than should be ex- 

 pected in accordance with the 

 dissociation hypothesis. The ex- 

 planation for this peculiarity 

 cannot be given. It is not un- 

 likely, however, that it may be 

 ascribed to the undissociated 

 molecules of acetic acid which 

 in a way serve as a reverse for 

 hydrogen ions. 



