RESPIRATION 55 



moisture in the atmosphere. The exhaled air is always 

 saturated, i.e. it has all the moisture it can possibly horld 

 at that temperature. 



5. The temperature of the air we breathe varies with 

 the time of day and season. The air as it passes from 

 the lungs has the temperature of the body, about ninety- 

 eight degrees (98' F.). 



Hence we are constantly taking from the air oxygen 

 and giving in exchange carbon dioxid and poisonous 

 organic substances. It is the presence of this organic 

 waste that makes it so dangerous to rebreathe the same 

 air and makes ventilation so important. 



1. Get a few small pieces of unslacked lime and put them into a 

 fruit jar. Fill the jar with water, and set it away for a day or two. 

 When the lime has all settled to the bottom, carefully pour off the 

 clear water into another bottle and label it limewater. 



2. Exhale air into the limewater and observe how milky the 

 limewater becomes. 



3. Exhale on a dry, clean mirror, and notice how the moisture 

 collects on it. Have you ever noticed how the moisture exhaled 

 from the lungs condenses on cold frosty mornings ? 



4. Exhale on a thermometer bulb for a few minutes and notice 

 that the mercury rises. 



54. Rate of Breathing. The number of times we 

 breathe per minute varies with age, position of body, 

 and exercise. The rate at different ages is about as 

 follows : 



Infants soon after birth 44 



Child from i to 5 years 26 



Youth, 15 to 20 years -20 



Early manhood, 20 to 25 years 19 



Manhood, 25 to 30 years 16 



Middle life to old age . . . 18 



