132 MEASUREMENTS OF GAS EXCHANGE 



about 1902, but Otto Warburg, the noted German biochemist, demon- 

 strated the general applicability of these principles to respiration and 

 photosynthesis. He was largely responsible for the wide adoption of the 

 manometric technique, and the method now bears his name. One should 

 not be surprised to hear, "How did you measure oxygen?" "Warburg." 

 Although we might expect more detailed communication between scien- 

 tists, this brief answer has conveyed sufficient information. 



The principle of manometry is relatively simple. We merely follow 

 the increase in pressure in a closed container as a gas is produced. The 

 behavior of the gas obeys the physicist's gas law, which is convention- 

 ally expressed by the following equation : 



PV = nRT (10-1) 



Here P is the pressure, V is the volume, n is the number of moles of gas, 

 and T is the absolute temperature (°K). R is the "gas constant," which 

 specifies the relationships of the other items. 



If the amount of gas (w) does not change, the equation becomes 

 equivalent to Charles' or Gay-Lussac's law, 



It tells us that if the amount of a gas and the temperature remain con- 

 stant, then an increase in pressure must be accompanied by a decrease 

 in volume. Or if the temperature and volume remain constant, a decrease 

 in the amount of gas will be accompanied by a decrease in pressure. 

 This latter case is used in the manometric method. Temperature and 

 volume are held constant, and the pressure is allowed to vary as the gas 

 is produced or consumed. 



In practice, we place the living cells or other experimental material 

 in a small glass container or vessel that can be coupled to a glass U-tube, 

 the manometer (see Fig. 10-1). A change in pressure will be indicated 

 by a difference in the height of fluid in the two arms of the U-tube. The 

 glass tubing is graduated in millimeters so that we can read the height 

 of the fluid. 



A glass stopcock in the manometer allows us to leave the vessel open 

 to the atmosphere until we are ready to start the measurements— which 

 means that the pressures inside and outside the container will be equal. 

 When we close the stopcock the living cells will be in a closed space on 

 one side of the manometer. The other side of the manometer is open to 

 the air. Thus we compare the pressure inside the vessel with that out- 



