FOR WAGGONER’S BIOLOGY 
21 
solved substance to move most easily? Why will these molecules 
tend to become uniformly distributed after a time? (See Wag¬ 
goner, Fig. 53.) To some extent the distribution of the potassium 
permanganate has been due to diffusion, but it is probable that 
other influences also have affected it. What have these been? 
Define diffusion. 
EXERCISE 23 
OSMOSIS 
For this experiment, a small tube similar to a thistle tube can 
be made easily by heating a test tube in the center by means of a 
Bunsen flame. When the glass is soft, the central portion of the 
tube may be drawn out to the desired size. The larger end of 
the small thistle tube thus produced may then be covered with the 
membrane from the inside of an eggshell. This apparatus serves 
well to illustrate osmosis. If an ordinary thistle tube is used, it 
is more practicable to use as a membrane the wall of the bladder 
or the outer wall of the intestine of a freshly killed beef or hog. 
The covering of fresh sausages, thoroughly cleaned, is also satis¬ 
factory. Animal parchment paper, such as is used in the chemical 
laboratory, will serve the same purpose. (Diffusion shells, used in 
dialysis, may be employed if available.) 
I. With a rubber band fasten the membrane tightly over the 
thistle tube. Place in the thistle tube a solution which has been 
made by dissolving some glucose in water. Lower this thistle 
tube into a beaker of pure water. (Arrange the whole as in the 
diagram, see Waggoner, Fig. 54.) Mark on the tube the level of 
the solution which is within. Note at intervals any changes which 
may occur in the level of this solution. After two hours, test the 
water which is in the beaker for glucose. What is the result? 
II. What causes the change in the level of the solution in the 
tube? What does diffusion have to do with the change in the com¬ 
position of the water in the beaker? What factor enters into the 
process in this experiment that was not present in the experiment 
on diffusion? How do root hairs take in soil water? 
