1917] BROOKS—PERMEABILITY 307 
In the experiments with living material the surface of these 
disks was quickly dried with filter paper, the disks (fig. 1, Z) placed 
between the ground ends of a pair of cells, and the joint made tight 
with a stiff cement consisting of a mixture of vaseline and beeswax 
(fig. 1, F). Thus there were formed two cells separated by a dia- 
phragm of Laminaria tissue. The cell supplied with the rubber 
tube and pinchcock (hereafter called the “lower cell’’) was then 
filled with solution and the pinchcock closed, care being taken that 
no air bubbles were included in the cell. The apparatus was then 
inverted and the upper cell filled with solution, covered to check 
evaporation (fig. 1, G), and set in a suitable 
support. During these operations each disk 
was in contact with the air less than two 
minutes, which was not sufficient to cause any 
appreciable drying-out of the tissue. 
In order to obtain dead tissue for experi- 
ments on the permeability of the intercellular 
substance, living disks were exposed, after cut- 
ting, to an atmosphere saturated with chloro- 
form vapor at room temperature for 16-24 
hours. They were next exposed to the air 
about one hour to allow the complete evapora- 
tion of any chloroform which remained in the 
tissue, and then placed in a large volume of sea oe 
water for about 24 hours to allow the establish- 
ment of equilibrium between the electrolytes of the sea water and 
those in the dead cells. At the end of this time the surface of the 
disks of tissue was dried with filter paper, and the apparatus set up 
as in the experiments with living material.. Tissue which had died 
a natural death gave results in every way similar to those given 
by tissue killed in this manner. 
The permeability of the tissue was shown by the rate of passage 
of salts through the diaphragm as shown by diminution of the 
difference of concentration between the solutions in the upper and 
lower cells. It is possible to measure rapidly, and with extreme 
accuracy, slight changes in the concentration of the solutions in 
either cell by determining the change in electrical conductivity. 
This method was therefore employed. 
