RESPIRATION 409 



air. Inspiration causes the lever to descend, expiration to ascend. Previous 

 graduation of the apparatus is necessary to determine the volumes breathed. 

 A graphic record of the volume changes is shown in Fig. 196. 



Respiratory Sounds. On applying the ear over the trachea and bronchi 

 there is heard during both inspiration and expiration a well-defined sound, 

 which is loud, harsh, and blowing in character, and which from its situation is 

 known as the bronchial sound. It is especially well heard between the 

 scapulae above the level of the fourth thoracic vertebra. This sound is 

 produced in the larynx, for with its separation from the trachea the sound 

 disappears. The cause of the sound is to be found in the narrowing of the 

 air-passage at the level of the vocal membranes, though the mechanism of 

 its production is uncertain. On applying the ear to almost any portion of 

 the chest-wall, but especially to the infrascapular area, there is heard during 

 both inspiration and expiration a delicate, sighing, rustling sound, which 

 from its supposed seat of origin, the air- vesicles or air-cells, is known as the 

 vesicular sound. This sound is supposed to be due to the sudden expansion 

 of the air-cells during inspiration a^H ^ thp fri^irm r>f ^A a j r 



THE CHEMISTRY OF RESPIRATION 



The general metabolic process as it takes place in the tissues involves 

 the assimilation of oxygen and the evolution of carbon dioxid. The former 

 is the first, the latter the last, of a series of chemic changes the continuance of 

 which is essential to the maintenance of all life phenomena. A constant 

 supply of oxygen and an equally constant removal of carbon dioxid are 

 necessary conditions for tissue activity. The blood is the medium by which 

 the oxygen is transported from the lungs to the tissues and the carbon dioxid 

 from the tissues to the lungs. The respiratory movements constitute the 

 means by which the oxygen of the air is brought into, and the carbon dioxid 

 expelled from, the lungs into the surrounding air. 



The exchanges between the blood and the tissues constitute internal 

 respiration, while the exchanges between the blood, the intra-pulmonic and 

 the atmospheric air, the result of the mechanic movements of the thorax, 

 constitute external respiration. The transfer of the oxygen by the blood 

 from the interior of the lungs to the tissues, and of the carbon dioxid from 

 the tissues to the interior of the lungs, is the outcome of a series of physical 

 and chemic changes which are related to the exchange of gases between the 

 air in the lungs and the blood, on the one hand, and the exchange of gases 

 between the blood and tissues, on the other hand. 



In consequence of the many and complex chemic changes which att 

 these gaseous exchanges, there arise changes in composition of: 



1. The air breathed. 



2. The blood, both arterial and venous. 



3. The tissue elements and the lymph by which they are surrounded 



The investigation of the nature of these changes, the mechanism of their 

 production, and their quantitative relations constitute the subject-matt 

 the chemistry of respiration. 



CHANGES IN THE COMPOSITION OF THE AIR 



Experience teaches that the air during its sojourn in the lungs undergoes 

 such a change in composition that it is rendered unfit for further breathing. 



