344 RESPIRATION. 



of the nostril, this respiratory action of the glottis is much more evident in 

 labored than in tranquil breathing. Indeed, in the latter case it is fre- 

 quently absent. The manner in which this rhythmic opening and narrow- 

 ing is effected will be described when we come to study the production of 

 the voice. Whether there exists a rhythmic contraction and expansion of 

 the trachea and bronchial passages, especially the smaller and more exclu- 

 sively muscular ones, effected by means of the plain muscular tissue of those 

 organs and synchronous with the respiratory movements of the chest, is un- 

 certain. 



CHANGES OF THE AIR IN RESPIRATION. 



280. During its stay in the lungs, or rather during its stay in the bron- 

 chial passages, the tidal air (by means of diffusion chiefly) effects exchanges 

 with the stationary air ; in consequence the expired air differs from inspired 

 air in several important particulars. 



The temperature of expired air is variable, but under ordinary circum- 

 stances is higher than that of the inspired air. At an average temperature 

 of the atmosphere, for instance at about 20 C., the temperature of expired 

 air is in the mouth 33.9, in the nose 35.3. When the external tempera- 

 ture is low, that of the expired air sinks somewhat, but not to any great 

 extent, thus at 6.3 C. it is 29.8 C. When the external temperature is 

 high, the expired air may become cooler than the inspired, thus at 41.9 it 

 has been found to be 38.1. The expired air takes its temperature from 

 that of the body, that is, of the blood, and this as we shall see later on, while 

 generally higher may, at times, be lower than that of the atmosphere. The 

 exact temperature of the expired air in fact depends on the relative tempera- 

 tures of the blood and inspired air, and on the depth and rate of breathing. 

 The change in temperature takes place not in the lungs but in the upper 

 passages, and chiefly in the nose and pharynx. 



281. The expired air is loaded with aqueous vapor. The point of 

 saturation of any gas, that is, the utmost quantity of water which any given 

 volume of gas can take up as aqueous vapor, varies with its temperature, 

 being higher with the higher temperature. For its own temperature expired 

 air is, according to most observers, saturated with aqueous vapor. The 

 moisture, like the warmth, is imparted not in the depths of the lung but in 

 the upper passages. The inspired air as it passes into the bronchia is already 

 saturated with moisture. 



282. The expired air contains about 4 or 5 per cent, less oxygen, and 

 about 4 per cent, more carbonic acid than the inspired air, the quantity of 

 nitrogen suffering but little change. Thus 



Oxygen. Nitrogen. Carbonic acid. 



Inspired air contains .... 20.81 79.15 0.04 



Expired .... 16.033 79.587 4.38 



The quantity of nitrogen in the expired air is sometimes found to be 

 slightly greater than as in the above table, but sometimes equal to, and 

 sometimes less than, that of the inspired air. 



In a single breath the air is richer in carbonic acid (and poorer in 

 oxygen) at the end than at the beginning of the breath. Hence, the longer 

 the breath is held, the greater the (artificial) pause between inspiration and 

 expiration, the higher the percentage of carbonic acid in the expired air. 

 Thus, by increasing the interval between two expirations to 100 seconds, the 

 percentage may be raised to 7.5. When the rate of breathing remains the 



