A STUDY OF THE PROBLEM OF WATER ABSORPTION. 37 
While this artificial cell differs from the living plant cell, 
the two are alike in several ways. The artificial cell takes up 
water from a dilute solution, but gives up water when trans- 
ferred from a dilute to a concentrated solution. The living 
cell takes up water from dilute solutions, but gives up water 
when placed in concentrated solutions. The layer of egg- 
albumen in contact with the paper bag certainly does not 
become differentiated so as to form a semi-permeable mem- 
brane, for egg-white is miscible with water in all proportions. 
Osmotic pressure is sometimes supposed to be demonstrated 
by breaking some of the shell from one end of an ordinary 
hen’s egg and then placing it in a tumbler of water. After 
a period of time the membrane surrounding the egg bulges 
at the point where the shell was removed, thus showing that 
a pressure has developed inside of the membrane. The mem- 
brane surrounding the egg may not be permeable to certain 
dissolved substances, but a paper bag that is quite permeable 
to these will serve just as well as the membrane when we wish 
to show that egg-albumen will take up water from dilute 
solutions. The pressure developed within the egg when it 
is placed in a tumbler of water is, for the most part, I believe, 
not a result of osmotic pressure, but a pressure due to the 
affinity that the colloids in the egg have for the water outside 
of the egg. Sometimes, in experiments like this, so much 
water is taken up that the membrane becomes greatly dis- 
tended and finally breaks. At this we need not be surprised. 
Fisher has shown that certain colloids have a strong affinity 
for water.1 
IV. DISCUSSION. 
That diffusion enters into the problems of absorption and 
secretion by living cells cannot be doubted, but that such 
cells maintain their turgor by virtue of osmotic pressure and 
are surrounded by semi-permeable membranes is pure assump- 
tion. We can explain turgor and water absorption without 
assuming the existence of a living membrane possessing the 
1 Fisher has shown that the colloids in the eye of the sheep are capable 
of taking up water from certain solutions until so much pressure is 
developed that they burst the strong coat surrounding the eye. 
