RESPIRATION 



25 



are larger than those in such a solid as glass or steel, but 

 they are still so tiny that they are invisible and they 

 must not be confused with holes. A membrane has no 

 " holes " in it. 



Influence of Pressure on Rate of Passage. — A gas 

 will pass through a membrane slowly or quickly accord- 

 ing to the number of particles that hit the membrane in 

 any given interval of time, and this depends of course on 

 the amount of gas that is present. The greater the 

 amount of gas in a given space, the greater will be the 

 number of particles that bombard the membrane in a 

 unit of time, the number that reach spaces, and the 

 number that pass through. This is but another way of 



Fig. 10.— A diagram illustrating the influence of pressure on the passage of gas. 



saying that the pressure of a gas determines the rapidity 

 with which it passes through a membrane (Fig. 10). 



Establishment of an Equilibrium. — Suppose (case 1) 

 two empty spaces of equal size, A and B, should be 

 separated by a membrane, and a gas should be intro- 

 duced into A (Fig. 11). Immediately its particles 

 would rush through the membrane and begin to fill 

 space B. As soon as a particle arrives in B it stands 

 a chance of again hitting the membrane and of getting 



