1915] OSTERHOUT—PERMEABILITY 243 
As the electrical conductivity of the tissue is a measure of the 
permeability of the protoplasm to ions, we may calculate the per- 
centage of increase of permeability by finding the change in con- 
ductivity. In the present instance it is more convenient to use the 
change in conductance without reducing this to specific conduc- 
tivity. The resistance at the start was 1020 ohms, but this includes 
the resistance of the apparatus with its contained sea water. 
Evidently this should be subtracted from the total resistance; the 
remainder will be called the net resistance. 
In this case the resistance of the apparatus was 250 ohms. The 
net resistance of the tissue at the start, therefore, was 1020—250= - 
77° ohms; the net conductance was 1+770=0.00130 mho. At 
the end of five minutes in NaCl the net resistance was 830—250= 
580 ohms; the net conductance was 1+580=0.00172 mho. The 
increase in permeability, therefore, amounts to 0.00172—0.00130= 
0.00042 mho, or 32.3 per cent.® 
It might be objected that this increase in conductance was not 
due to an increase in permeability but to an increase in the ions 
of sodium chloride, to which the tissue might be assumed to be 
normally more permeable than to some of the other ions of the sea 
water. This, however, cannot be the case, as is shown by the 
following experiment. Tissue having a resistance of 1020 ohms 
was placed in a mixture of 1000 cc. NaCl 0.52M+20 cc. CaCl, 
0.278M. The resistance remained at 1020 ohms in this mixture. 
The tissue was then transferred to NaCl 0.52M for five minutes. 
At the end of this time the resistance had fallen to 860 ohms; on 
being placed in sea water the resistance rose to the normal and so 
remained for some time. 
In this case the resistance of the apparatus was 230 ohms. The 
net resistance at the start was 1020—230= 790 ohms; and the net 
n the previous paper it was suggested that the tissue should be killed, sapien the 
resistance. It seems better, however, to take the resistance of the apparatus after 
the tissue has been removed, to subtract this from the total, and call the remainder - 
the net resistance. 
‘Complete recovery after such a large increase of Dasemgar ie is not wtng 4d 
obtainable unless the material is in good condition and is freshly coll 
such material a lot will occasionally be found which shows poor aaa. 
