CHARACTER OF THE CELL MEMBRANE AFTER DEATH 119 
amount of solution within until some of the solution is forced 
up the tube. The solution rises in the tube because the increase 
in the amount of solution within the bladder requires more space, 
and is, therefore, accompanied by an increase in pressure against 
the wall of the bladder. This pressure, which in this case de- 
pends upon the concentration of the sugar solution in the bladder, 
might become so great as to burst the bladder, if no tube for an 
outlet were provided. This pressure, known as osmotic pressure, 
has been found to follow quite well the laws governing gas pres- 
sure. Consequently, if the number of molecules of the dissolved 
substance contained in a certain volume of the solution is known, 
the osmotic pressure can be calculated. Thus 342 grams of Cane 
sugar in 1 liter of solution (called a gram-molecular solution) will 
exert a pressure of about 22.3 atmospheres or 336 lbs. and in 
whatever proportion the number of grams is increased or de- 
creased, the pressure is altered in a similar proportion. Osmotic 
pressure in cells, where it is called turgor pressure, is usually not 
less than 50 lbs. and often more than 100 lbs. The rigidity of 
organs such as leaves, soft stems, and roots is largely due to turgor 
pressure, as can be easily shown by immersing strips of a fresh 
Beet or Radish in a strong solution where they lose water and 
become flaccid. The wilting in leaves when exposed to excessive 
evaporation is due to the loss of turgor pressure, which occurs 
whenever cells lose water more rapidly than they absorb it: The 
preservative value of such substances as salts and sugars when 
applied to meats and fruits depends largely upon the withdrawal 
of water from the micro-organism, so that they can not become 
active. Wilted cells, if not dead, wil! also draw in water and again 
become turgid when put in contact with moisture. In this way 
flowers are revived by placing their stems in water, and Cucum- 
bers, Lettuce, and Celery are made crisp by putting them in cold 
water. Sometimes, as the pollen of some plants illustrates when 
immersed in water, the pressure becomes so great that the cells 
burst. Even fruits, such as Plums, sometimes burst on the trees 
from this cause when the weather is warm and moist. 
The Character of the Cell Membrane After Death. — With the 
death of the cell, the cell membrane ceases to be an osmotic mem- 
brane and thus becomes permeable to all substances in solution. 
After the cell membrane is dead substances pass through it, 
either into or out of the cell, almost as easily as through a piece of 
