200 PHYSIOLOGY FOR DENTAL STUDENTS. 



Cent.) will dissolve to the amount of one c. c. in one c. c. of water. 

 Under like conditions only 0.04 c. c. of oxygen will be dissolved, 

 The coefficient of solubility of carbon dioxide is therefore 1.0 and 

 of oxygen 0.04. 



The amount of gas which will go into solution in water depends 

 on three factors : the temperature of the water, the solubility of 

 the gas in water, and the pressure which the gas exerts on the 

 surface of the water. As a rule, -the higher the temperature of the 

 water, the less gas will go into solution, or in other words, the 

 solubility of a gas varies inversely with the temperature. 



The pressure which a gas exerts on the surface of a fluid is 

 expressed in terms of millimetres of mercury. The pressure of an 

 atmosphere is equal to 760 mm. of mercury at sea level and 15.5 

 degrees temperature. This is known as the standard barometric 

 pressure. If in place of having pure gases over a fluid, a mixture 

 of several gases be present, then we find the solubility of each of 

 the gases varying directly with the pressure it exerts on the sur- 

 face of the fluid. Suppose that in place of exposing a cubic centi- 

 metre of water to oxygen at 760 mm. pressure, we expose it to 

 oxygen at a pressure of 152 mm. mercury the normal pressure 

 of oxygen in the air 1/5 of an atmosphere) it would absorb 1/5 

 of .04 c. c. or .008 c. c. of oxygen. The presence of other gases 

 does not enter into consideration, for according to Dalton-Hen- 

 ry's law, when two or more gases are mixed together, each of 

 them produces the same pressure as if it separately occupied 

 the entire space and the other gases were absent. When the fluid 

 has taken up all the gas it can, an equilibrium becomes estab- 

 lished between the gas in the atmosphere and the gas within the 

 fluid. The pressure which the gas in the fluid exerts on the gas 

 in the atmosphere is known as the tension of the gas, and equals 

 the pressure of the gas in the outside atmosphere to which it is 

 exposed. This can be easily measured. 



Since the pressure of the oxygen in the air in the lungs is less 

 than that in the outside atmosphere, it is apparent that if the 

 blood should carry the same amount of oxygen as water, the 

 amount would be very sniall indeed. Analysis of the amount of 

 oxygen in arterial blood shows that it contains 40 times the 



