286 Del/. — Studies of Protoplasmic Permeability by 
a cork in the neck of the flask, two of which are governed by the three-way 
tap at K, whilst the third, I, is an outflow, the level of which at M determines 
the rate of flow of the liquid through the chamber and coil ; the side tube O 
is an additional outlet for more rapidly emptying the chamber. 
By means of the tap K a liquid entering through z can be diverted at 
will to the tube leading to the coil H or to the tube J which acts as a by- 
pass ; or the tap can be turned so that no liquid can enter from Z. The 
whole flask is packed in cotton-wool or ice for high and low temperatures 
respectively, and is encased in a wooden box to diminish further loss of heat 
by radiation. The box is raised on a wooden block P during an experiment 
when the plant cylinder is immersed in water in the conical flask. The block 
can be removed by a handle when the chamber is to be lowered ; the nozzle 
can then be adjusted or removed, together with its clamp, to receive a new 
piece of tissue. When an experiment is being made, a thermometer is also 
suspended in the chamber so that its bulb stands close by the plant 
cylinder. (In the figure this is shown on the opposite side.) 
The flow of liquid entering z is determined by two three-way taps 
placed one on either arm of a double Y-tube and connected with delivery 
tubes x and Y leading from the solutions. X and Y are further connected 
with long flat coils of glass tubing (not shown in the diagram), and both 
are surrounded with a large water-bath, Q, kept at constant temperature by 
means of a thermostat. A current of water or solution passes from the 
aspirators along one of the coils where it acquires the temperature of the 
water-bath. It then enters the tube X or Y and can be diverted at will to 
either the outer tubes T or s leading to the chamber, or to the inner tubes 
U or R leading to the outflow N. It is therefore possible to have two streams 
of liquid running at the same rate, traversing an equal distance through the 
same water-bath and hence acquiring the same temperature ; and either of 
these liquids can be turned through the plant cylinder immediately without 
any perceptible change in temperature. 
Section III. Procedure in a Typical Experiment. 
The optical lever was first adjusted relative to the source of light so that 
a sharply defined cross wire in a bright field of light was thrown upon 
the distant millimetre scale ; the lever, light-source, and scale remained in 
these positions throughout the experiments and together gave a magni- 
fication of nearly 350 diameters. This was estimated directly by measur- 
ing the deflexion of a spot of light on the scale when a vertical thread 
attached to the middle arm of the optical lever was depressed (by hang- 
ing on it a very small piece of fine wire) through a distance of 1 mm. 
as measured by a vertical scale immediately behind it. 
A small counterpoise attached to the free arm of the optical lever 
was adjusted by trial until the tension in the plant cylinder, when fixed 
