CELL PENETRATION BY ACIDS. 



V. Note on the Estimation of Permeability Changes. 



By W. J. CROZIER. 



(Contributions from the Bermtida Biological Station for Research, No. 139, and 

 from the Zoological Laboratory, Rutgers College, New Brunswick.) 



(Received for publication, April 10, 1922.) 

 1. Effects of Tension. 



In view of the fact that qualitative studies regarding permeability 

 have sometimes been based upon experiments involving intense 

 muscular activity in the tissue examined, I thought it worth while 

 to measure the effect of stretching upon the rate with which acids 

 penetrate the indicator-containing tissue of the nudibranch Chro- 

 modoris (cf. Crozier, 1916 a). 



A piece of the mantle fold, about 2 cm. in length by 0.5 cm. in 

 breadth, was freshly secured by cutting from an individual suf- 

 ficiently large to supply several such pieces. The piece was then 

 adjusted in a holder, sketched in Fig. 1. This was accomplished 

 by tying to either end a short ligature of waxed thread. One of 

 the ligatures was made fast at a, while the other, longer, one was 

 passed over the groove c. The longer thread carried at its free end 

 a mass which in the different tests was varied from 5 to 50 gm. 

 The tissue, being fixed in this manner, was lowered into the trough, 

 A, containing an acid solution. The time required for the internal 

 color change to be brought about was measured with a stop-watch, 

 while the first evidence of pigment loss could be accurately recognized 

 by watching the edge of the tissue through a horizontal microscope. 

 A slip of milk-glass, mounted back of the tissue, increased the 

 precision of the observations. 



By employing a strip of the mantle about 2 cm. in length, there was 

 secured an area in the center of the strip which was free from com- 

 plications due to the presence of tight ligatures at either end. This 

 was checked by experiments in which the tissue, with tlie threads 

 made fast, was allowed to hang freely without any attached weights. 



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