728 CELL PENETRATION BY ACIDS. V 



£a;/'mwe«^ ^JJ. J.— Individual A, 6 cm. long; B, 11 cm. long; 0.05nHNO3;20°C. 



This effect can hardly be referred to the contraction of the tissue ; 

 the mantle fragments relaxed when the electrodes were removed, 

 before being placed in acid; and they always contracted upon im- 

 mersion in acid, whether previously stimulated or not. Nor can 

 the extruded mucus be directly involved, for the same reason. More- 

 over, as pointed out beyond, mucus extrusion also occurs under the 

 influence of chloroform, which has an opposite effect upon pene- 

 trability. 



When a small spot upon a fair sized piece of the nudibranch in- 

 tegument was stimulated, and the whole then placed in acid, the 

 increased penetrability was manifest merely upon the immediate 

 site of excitation. Thus, in one experiment with 0.05 N HNO3, a 

 stimulated area turned pink in 2.45 minutes, while the general 

 surface of the tissue did not do so until 3.20 minutes had passed, in 

 spite of the fact that mucus discharge had occurred over the entire 

 surface. 



The method of observation is such that the results may not be 

 interpreted in terms of "permeability," since the intracellular color 

 change serving as an index of acid penetration is dependent upon the 

 relation of the pigment to the rest of the cell contents; this relation 

 might be altered by excitation of the epithelium. Nevertheless, it 

 is entirely probable that in these tests the penetrability of the proto- 

 plasm toward acid is markedly increased as the result of faradic 

 stimulation. 



