CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE MUSEUM OF 

 COMPARATIVE ZOOLOGY AT HARVARD COLLEGE, E. L. MARK, DIRECTOR. 

 NO. 212. 



REACTIONS OF FROGS TO CHLORIDES OF AMMONIUM, 

 POTASSIUM, SODIUM, AND LITHIUM 



LAWRENCE W. COLE 



The experiments herein recorded were designed to test reactions 

 of the common leopard frog, Rana pipiens Schreber, to solutions 

 of the chlorides of ammonium, potassium, sodium, and lithium. 

 As these reactions were obtained from frogs whose brains had been 

 destroyed, they are, strictly speaking, spinal-cord reactions and 

 dependent, therefore, on spinal nerves. Whether or not they can 

 be related to taste will be discussed toward the close of this paper. 

 The subject was suggested to me by Professor G. H. Parker and 

 the work was done under his direction. 



A series of preliminary experiments showed that the lower limit 

 of the susceptibility of the frog's skin to these salts is not far from 

 a solution of m./2 strength. Even the most responsive specimens 

 of R. pipiens reacted only once or twice tom./2 solutions of the 

 chlorides of sodium or of lithium. They reacted very frequently, 

 however, to ammonium and potassium solutions of that strength. 

 3 m. solutions were the strongest ones tried, for larger amounts of 

 some of these chlorides do not dissolve completely in water. 



Merck's salts were used in the preparation of the solutions and 

 each solution was titrated against one of potassium chloride taken 

 as a standard until results within 2 per cent of accuracy were ob- 

 tained. The titration was done in silver nitrate with potassium 

 chromate as an indicator. 



Freshly prepared brainless frogs were suspended by the lower 

 jaw from a hook on a lever apparatus such as had already been 

 used by Parker and Metcalf ('06) for similar experiments on earth- 

 worms. Essentially the same method had previously been em- 



