REACTIONS OF NECTURUS TO STIMULI THROUGH SKIN 85 



is induced. Necturus is most sensitive to nitric acid at all 

 concentrations and hydrochloric gives the weakest response, 

 except acetic. The reactions were found to become weaker and 

 fewer as the acid was diluted. The gills were in nearly all 

 cases the most sensitive region, with the nostrils, head, and 

 tail following in order. Stimulation of the nostril, with a ten 

 per cent solution usually produced an expulsion of air from the 

 nostrils and mouth in addition to locomotion. The limit of 

 reaction for hydrochloric, sulphuric and nitric acids was 0.015 

 and for acetic 0.01 per cent. 



TABLE I* 

 Reactions to 10% Hydrochloric Acid 



* Explanation of the Tables. — For convenience, several signs have been employed 

 in the tables. They indicate as follows: F, forward; B, backward; X, animal 

 turned around; O, no reaction. A letter not followed by a number indicates a 

 very slight movement, such as a jerk. The numbers I, II, III and IV indicate 

 the four individuals under experiment. The reactions are noted for seven regions 

 of the body, as indicated at the top of each table, making a total of twenty-eight 

 reactions of four individuals in each concentration. The reactions are measured 

 as inches of locomotion, as described elsewhere, and the average is for total move- 

 ment, backward and forward, for each region stimulated. 



