248 NASAL BREATHING. 



Supposing, however, respiration to have been fully established after birth, and 

 air to have freely entered the lungs, if a manometer be placed in connection with 

 the trachea and the chest b'e opened, the manometer will register a pressure of 

 6 mm. Hg., due to the collapse of the elastic lungs. Bernstein supposes that the 

 thorax assumes a new permanent form, due to the first respiratory distension; it 

 is as if, owing to the respiratory elevation of the ribs, the thorax had become 

 permanently too large for the lungs, which are, therefore, kept permanently 

 distended, but collapse as soon as air passes into the pleura. When a lung has 

 once been filled with air, it cannot be emptied by pressure from without, as the 

 small bronchi are compressed before the air can pass out of the alveoli. The 

 expiratory muscles cannot possibly expel all the air from the lungs, while the 

 inspiratory muscular force is sufficient to distend the lungs beyond their elastic 

 equilibrium. Inspiration distends the lungs, increasing their elastic tension, while 

 expiration diminishes the tension without abolishing it. 



119. Appendix to Respiration. 



Nasal Breathing. During quiet respiration, we usually breathe 

 or ought to breathe through the nostrils, the mouth being closed. 

 The current of air passes through the pharyngo-nasal cavity so that 

 in its course during inspiration, it is (1) warmed and rendered moist, and 

 thus irritation of the mucous membrane of the air-passages by the cold 

 air is prevented ; (2) small particles of soot, or other foreign substances 

 in the air, adhere to, and become embedded in the mucus covering the 

 somewhat tortuous walls of the respiratory passages, and are carried 

 outwards by the agency of the ciliated epithelium of the respiratory 

 passages ; (3) disagreeable odours and certain impurities are detected by 

 the sense of smell. 



If a lung be inflated, air constantly passes through the walls of the alveoli and 

 trachea. This also occurs during violent expiratory efforts (cutaneous emphysema 

 in whooping-cough), so that pneumo-thorax may occur (J. R. Ewald and 

 Roberts). 



Pulmonary (Edema, or the exudation of lymph or serum into the pulmonary 

 alveoli, occurs: (1) When there is very great resistance to the blood-stream in 

 the aorta or its branches, e.g., by ligaturing all the arteries going to the head 

 (Sig. Mayer), or the arch of the aorta, so that only one carotid remains pervious 

 (Welch). (2) When the pulmonary veins are occluded. (3) When the left 

 ventricle, owing to mechanical injury, ceases to beat, while the right ventricle 

 goes on contracting (p. 75). These conditions produce at the same time anaemia 

 of the vaso -motor centre, which results in stimulation of that centre, and conse- 

 quent contraction of all the small arteries. Thus, the blood-stream through the 

 veins to the right heart is favoured, and this in its turn favours the production of 

 redema of the lungs. 



120. Peculiarly Modified Respiratory Movements. 



(1.) Coughing. Consists in a sudden violent expiratory explosion after a 

 previous deep inspiration and closure of the glottis, whereby the glottis is forced 

 open and any substance, fluid, gaseous or solid, in contact with the respiratory 

 mucous membrane is violently ejected through the open mouth. It is produced 



