1 82 NASAL BREATHING. 



ampulla on its lower end into the cesophagus, so that the ampulla came to lie opposite the 



S)sterior mediastinum. The sound was connected with a registering tambour or manometer, 

 uring inspiration the manometer fell, and during inspiration it rose.] 



Even the greatest inspiratory or expiratory pressure is always much less than the blood- 

 pressure in the large arteries ; but if the pressure be calculated upon the entire respiratory 

 surface of the thorax, very considerable results are obtained. 



Pneumatometer. This instrument of Waldenburg is merely a mercurial manometer fixed to a 

 stand, and connected to an elastic tube with a suitable mouthpiece, which is fitted over the 

 mouth and nose, while the variations of the Hg can be read off on a scale. [In the male, the 

 expiratory pressure is 90-120 mm. Hg, and the respiratory 70-100. The relation of the 

 pressures during expiration and inspiration is more important than the absolute pressure.] 

 The inspiratory pressure is diminished in nearly all diseases where the expansion of the lung is 

 impaired [phthisis], or the expiratory pressure is diminished, as in emphysema and asthma. 



Effects of the first Respiration on the Thorax. Until birth, the airless lungs are completely 

 collapsed (atelectic) within the chest, and fill it, so that on opening the chest in a dead foetus, 

 pneumo-thorax does not occur (Bernstein). 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 be 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 pre- 

 vented ; (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 epi- 

 thelium 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. B. Ewald and Robert). 



Pulmonary (Edema, or the exudation of lymph 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 or the arch of the aorta, so that only one carotid 

 remains pervious. (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 ( 47). 

 These conditions produce at the same time anaemia of the vaso-motor centre, which results in 

 stimulation of that centre, and consequent 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 oedema of the lungs. [The injection of muscarin rapidly causes pulmonary 

 oedema, due to the increase of pressure and slowing of the blood-stream in the pulmonary capillaries. 

 It is set aside by atropin ( W.einzweig, Grossmann).] 



120. 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 res- 

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

 tarily or reflexly ; in the latter case, it can be controlled by the will only to a limited extent. 



[Causes. A cough may be discharged reflexly from a large number of surfaces: (1) A 

 draught of cold air striking the skin, especially of the upper part of the body. This may cause 

 congestion of blood in the air-passages, this in turn exciting the cough. (2) More frequently 

 it is discharged from the respiratory mucous membrane, especially of the larynx, the sensory 

 branches of the vagus and the superior laryngeal nerve being the afferent nerves. A cough 

 cannot be discharged from every part of the larynx : thus there is none from the true vocal cords, 



