CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF 

 THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD 

 COLLEGE, E. L. MARK, DIRECTOR. — No. 2n. 



THE REACTIONS OF EARTHWORMS TO ACIDS. 



By S. H. Hurwitz. 



Presented by E. L. M:^rk. May 11, 1910. Received May 18, 1910. 



The present investigation was made to ascertain the influence of 

 inorganic and organic acids on the responses of the common manure 

 worm, Allolobophora foetida (Sav.). Apart from its specific applica- 

 tion, this problem bears upon the more general one of the relation of 

 electrolytes — acids, bases, and salts — to physiological processes. For 

 the suggestion of this problem and for much valuable advice as to 

 method and interpretation, I am greatly indebted to Professor G. H. 

 Parker. 



The sense of taste even in man is not well understood. What its na- 

 ture in an invertebrate may be, is only a matter of conjecture. Experi- 

 ments designed to determine the relation between the chemical nature 

 of solutions of acids to the sensations of taste in man, and especially 

 to ascertain how closely the sensation corresponds to the degree of 

 dissociation were made by Kahlenberg ('98) and by Richards ('98). 

 It was my purpose to ascertain to what extent the conclusions reached 

 in a study of human taste were applicable to a typical invertebrate like 

 the earthworm. 



The modern theories of solutions lead to the conclusion that the 

 taste of a solution of an electrolyte must depend upon the taste of its 

 ions, its undissociated molecules, or both ; furthermore, the taste of a 

 solution in which ionization is practically complete should be due 

 simply to its ions. At dilutions of xrcr such as were used in the pres- 

 ent investigation, strong acids, at least, would be almost conipletely 

 dissociated. And their sour taste or stimulating value has been shown 

 both by Kahlenberg and by Richards to depend upon hydrogen ion. 

 It was further shown by Richards that the degree to which such acids 

 stimulate is directly determined by the number of hydrogen ions. 



For the purpose of the present study, three inorganic and one or- 

 ganic acid were used ; they were hydrochloric, nitric, sulphuric, and 



