JANUARY 19, 1912] 
were packed together (like a roll of coins) 
into a solid cylinder from 50 mm. to 100 mm. 
long. They were firmly held in place by 
glass rods arranged to make a hollow cylinder 
which closely fitted over the outside of the 
solid cylinder of tissue. Spaces between the 
rods allowed free access of the solution to the 
living tissue. At each end of the cylinder of 
tissue was placed a block of hard rubber con- 
taining a platinum electrode covered with 
platinum black; by means of a screw these 
blocks could be pressed with considerable 
force against the opposite ends of the cylinder 
of living tissue. The only substances which 
came into contact with the solution were hard 
rubber, glass, the electrodes and the living 
tissue. Details of construction will be given 
in a subsequent paper. 
The current after leaving the electrodes 
traversed the solution for a very short distance 
and then passed directly into the living tissue. 
The same solution which bathed the electrodes 
was also present between the disks of living 
tissue in the form of thin films. The surface 
in and out of which ions were forced by the 
current amounted to from 26,500 to 53,000 
‘sq. mm. 
The measurements were made in the usual 
manner by means of a Wheatstone bridge. 
‘The solutions were brought to the same tem- 
perature before measuring except that in the 
-ease of small deviations the proper correction 
was made. 
The usual method of procedure was to place 
the cylinder of disks in the solution, clamp 
the electrode carriers firmly against both ends 
-of it, lift it out of the solution and read the 
resistance as soon as the superfluous liquid 
had drained from the tissue. 
A preliminary series of experiments showed 
that the material remained to an extraordinary 
‘degree uninjured by the action of the cur- 
rents employed as well as by the additional 
treatment involved in the experiments. In 
the first experiments the material was usually 
left immersed in sea water in the apparatus 
for 24 hours. During this period 12 readings 
were taken (the current passing for about 
-two minutes each time) and the disks were 
SCIENCE 
113 
12 times taken out and then replaced in the 
apparatus. At the end of the 24 hours the 
resistance to the current remained unchanged 
(if injury had occurred the resistance would 
have been diminished) and there was no indi- 
cation either macroscopic or microscopic that 
the cells were injured. 
If the plasma membrane and the cell wall 
presented no obstacle to the passage of ions 
we should expect the resistance of a cylinder 
of living tissue to be practically that of a 
similar cylinder full of sea water. It was 
found that a cylinder of living tissue had a 
resistance of 1,100 ohms (all the figures given 
in this paper refer to readings taken between 
18° C. and 18.2° C.) while that of a cylinder 
of sea water of equal size was 320 ohms. To 
ascertain whether this excess of resistance was 
due to living protoplasm or to cell walls the 
protoplasm was killed by adding sufficient 
formalin to the sea water to make a 2 per cent. 
solution. In other experiments the disks were 
killed by careful drying. Im all cases the 
resistance after killing fell to about 320 ohms. 
These experiments demonstrated in the clear- 
est manner that the ions penetrated very much 
less rapidly into living cells than into dead 
protoplasm or into cell walls. 
Experiments were then made to determine 
the rate of penetration of various ions. As 
the treatment was the same in all cases it will 
suffice to describe a typical experiment deal- 
ing with NaCl and CaCl,. . 
The material was first tested in sea water 
and found to have a resistance of 1,100 ohms. 
After remaining four hours in sea water the 
resistance was unchanged. The material was 
then transferred to NaCl .52 M which had 
the same temperature as the sea water and the 
same conductivity (as determined by numer- 
ous careful tests). The electrode carriers 
were unclamped and moved apart. Each disk 
was then seized in turn by the forceps and 
moved back and forth in the solution so as to 
wash out the sea water and replace it by the 
solution of pure NaCl. This was repeated 
several times. It was thus possible to rinse 
each disk thoroughly in the solution without 
removing it from the apparatus or changing 
