1 6 THE MECHANISM OF LIFE 



contains CO grammes of urea per litre, while a normal 

 solution of sugar contains 312 grammes of sugar per litre. 



The Dissolved Substance is a Gas. — Van f Hoff, using the 

 data obtained by the botanist Pfeffer, showed that the 

 dissolved matter in a solution behaved exactly as if it were 

 a gas. The analogy is complete in every respect. Like the 

 gaseous molecules, the molecules of a solute are mobile with 

 respect to one another. Like those of a gas, the molecules 

 of a solute tend to spread themselves equally, and to fill 

 the whole space at their disposal, i.e. the whole volume of 

 the solution. The surface of the solution represents the 

 vessel containing the gas, which confines it within definite 

 limits and prevents further expansion. 



Osmotic Pressure. — Like the molecules of a gas, the mole- 

 cules of a solute exercise pressure on the boundaries of the 

 space containing it. This osmotic pressure follows exactly the 

 same laws as gaseous pressure. It has the same constants, and 

 all the notions acquired by the study of gaseous pressure 

 are applicable to osmotic pressure. Osmotic pressure is in fact 

 the gaseous pressure of the molecules of the solute. 



When a gas dilates and increases in volume, its temperature 

 falls, and cold is produced. Similarly, when a soluble substance 

 is dissolved, it increases in volume, and the temperature of the 

 liquid falls. This phenomenon is well known as a means of 

 producing cold by a refrigerating mixture. 



The phenomena of life arc governed by the laws of gaseous 

 pressure, since all these phenomena take place in solutions. 

 The fundamental laws of biology are those of the distribution 

 of substances in solution, which is regulated by the laws of 

 gaseous pressure, since all bhese laws are applicable also to 

 osmotic pressure. 



Boyle's Law. — When a gas is compressed its volume is 

 diminished. If the pressure is doubled, the volume is reduced 

 to one-half. The quantity V x P, that is the volume multiplied 

 by the pressure, is constant. 



Gay-Lussac's Laic. — For a difference of temperature of 

 a degree Centigrade all gases dilate or contract by ^] .. of 

 their volume at 0° Centigrade. 



