INJURY AND RECOVERY 85 



than when lanthanum was used, the experiment was per- 

 formed twice daily on each of the five successive days. 

 On the sixth day the material was in as good condition as 

 the control, and had the same resistance. 



It is evident, therefore, that the conductivity may be 

 greatly decreased and then restored to the normal several 

 times on successive days, without any trace of injury. 



Experiments on dead tissue (killed by heat or by 

 formalin or allowed to die a natural death) showed that 

 the results described above are due entirely to the 

 living cells. 



A very marked decrease of permeability may be pro- 

 duced by a considerable variety of other salts. The 

 addition of these salts in solid form simultaneously 

 increases the conductivity of the solution and decreases 

 the conductivity of the tissue. This affords the most 

 convincing proof that the change in the conductivity of 

 the tissue in these experiments cannot be due to any 

 cause other than a change in permeability ; for the concen- 

 tration of the ions of the sea water remains unchanged, 

 and if they were able to penetrate as freely as they did 

 before the addition of the salt, the resistance w r ould not 

 increase. It would, in fact, diminish on account of the 

 increased conductivity of the solution held in the cell 

 walls, as is clearly shown by experiments on dead tissue. 



It may be remarked incidentally that these experi- 

 ments effectually dispose of the possible objection that the 

 current passes between the cells, but not through them. 

 Were this objection well founded, the decrease in con- 

 ductivity could be explained only as the result of a 

 decrease in the size of the spaces between the cells. This 

 decrease could not be brought about except by greatly 

 reducing the thickness of the cell walls. Both macroscopic 



