726 



CELL PENETEATION BY ACIDS. 



exposure to the air has a very marked influence in the direction of 

 decreasing its penetrability. The penetrability of isolated fragments 

 of the Chrojnodoris mantle kept in sea water remained very nearly 

 constant for some 24 hours after their removal. 



The influence of tension is equally apparent in relation to dif- 

 fusion of pigment from the mantle tissue. In one set of experi- 

 ments, which may be cited as typical, the following observations 

 were recorded: 



Experiment 9.26b. — Mantle tissue from two nudibranchs 8.5 cm. long; 0.01 N 

 dichloroacetic acid; 25°C. 



The observations on the outward diffusion of pigment are difficult 

 to summarize, because it is necessary to choose for comparison 

 individuals with closely agreeing pigmentations. There was no 

 doubt of the qualitative result, however, which was clearly that the 

 rate of spontaneous pigment diffusion, in acid, is greater when the 

 tissue is stretched. Moreover, the effect of tension was usually 

 greater with respect to pigment diffusion than in relation to penetra- 

 tion of acid (as evidenced by color change). The outcome of these 

 tests may be held to indicate that under tension the resistance of a 

 protoplasmic surface to the diffusion of electrolytes undergoes a 

 (more or less reversible) decrease.^ The experiments may then have 

 an interesting connection with Carlson's (1907) finding in the 



^ What role may be occupied by an actual thinning-out of the cells of the 

 tissue stretched in the present experiments, it is difficult to decide; my chief 

 purpose is to point out, merely, the complication introduced into "perme- 

 ability" studies by the presence of tractive forces. 



