INJURY AND RECOVERY 83 



falling off was also shown by the control, which remained 

 in sea water through the experiment, it was not due 

 to NaCl but to other causes. The results are shown 

 in Fig. 34. 



Electrolytes may also cause a reversible decrease in 

 permeability. The simplest way of demonstrating this is 

 by means of the following very striking experiment. The 

 net resistance of a cylinder of living tissue in sea water 

 was found to be 500 ohms. It was tested an hour later 

 and found to be the same. Sufficient La(N0 3 ) 3 was then 

 added in solid form to make its concentration 8 in the sea 

 water 0.02 M. After 5 minutes the resistance rose to 

 130%. In order to ascertain whether this change in per- 

 meability is reversible, the tissue was replaced in sea 

 water. In the course of an hour its resistance returned 

 again to the original value. 9 The experiment was 

 repeated three times on the same lot of material with 

 practically the same result ; it was then allowed to stand 

 over night in sea water. On the following day there was 

 no appearance of injury, and the resistance was the same 

 as that of the control, which had remained in sea water 

 throughout the experiment. The tissue was then placed 

 in the sea water plus lanthanum and left until its resist- 

 ance had increased 100 ohms; it was then put back into 

 sea water and left until the resistance fell to nearly 

 normal. This was repeated three times, and the tissue 

 was then allowed to stand over night in sea water. On the 



8 The concentration was reduced by the precipitation of a small amount 

 of La, (SO^a; this had practically no influence on the subsequent result, 

 since the outcome is the same if we use in place of sea water a mixture 

 of 1000 c.c. NaCl 0.52 M + 20 c.c. CaCl 2 0.278 M, in which case no 

 precipitate is formed. It should be noted that the addition of lanthanum 

 chloride has the same effect as the addition of lanthanum nitrate. 



9 If the material is left in sea water plus La(N0 3 ) 3 the increased re- 

 sistance is maintained for a long time. 



