that 13.4 g of water is formed when lOOkcal of barley (corresponding to 25 g of dry 

 barley) is metabolized. This amount far exceeds the amount of preformed water at 

 all humidities and is therefore the main intake of water for the animals living on 

 dry grain. It cannot be increased in any mysterious way by desert animals as it 

 has sometimes been suggested. The desert rodents can, however, economize with 

 their water to a considerably higher degree than other mammals, as shall be shown 

 in the following. 



Output 



Evaporation: The evaporation from the respiratory tract is proportional to the venti- 

 lation which again is proportional to the oxygen uptake. In man the exhaled air is 

 saturated with water vapour at a temperature of about 33°C which is slightly below 

 the rectal temperature. When completely dry air is inspired all the moisture that is 

 necessary to bring this air to saturation at 33°C must evaporate from the respiratory 



176 



