XII 



MECHANICS OF EESPIEATION 



437 



firmed on the schema) that the inspiratory movements assist the 

 venous (and lymphatic) current, and favour the diastolic filling of 

 the heart, while the expiratory movements facilitate the arterial 

 current and systolic evacuation of the heart. 



XIV. The rhythmical respiratory movements suffer various 

 modifications, in abnormal or unusual conditions, or to satisfy 

 various temporary needs or occurrences, or, lastly, as the motor 

 expression of special sentiments of pleasure or pain, fatigue, ennui, 



FIG. -201. Schema to demonstrate effect of strong positive and negative intrathoracic pressures 

 upon heart and blood-stream. (Landnis.) D, D', stout elastic membrane which closes the 

 floor of a bell-jar, and can be pushed up or down by a handle, to imitate expiration and 

 inspiration. P, P, and P' P', two thin rubber balloons, to imitate the lungs, communicating 

 with a central tube, representing the trachea, which passes through the centre of the bell- 

 glass, with tap r to simulate the glottis. CO', a rubber ball, to represent the heart, com- 

 municating on one side with the tube V, V, which represents the afferent vessels of the heart 

 (provided with a valve that opens in inspiration and closes in expiration), on the other with 

 the tube A, A', representing the efferent artery, (with valve that, closes in inspiration and 

 opens in expiration). When ? is closed, the manometer M shows a marked diminution of 

 pressure, with dilatation of heart and lungs, in inspiration ; in expiration it shows marked 

 increase of pressure, while the heart and lungs retract. 



sleep, etc. The principal forms may be briefly summarised as an 

 appendix to the mechanics of respiration. 



When there are mechanical impediments to the thoracic or 

 abdominal respiratory movements, e.g. plaster bandages applied to 

 the chest or epigastrium, the activity of the diaphragm or the 

 levator muscles to the ribs, respectively, is exaggerated, and the 

 rhythm becomes deeper and slower. 



When the respiratory movements cause or increase pains in 

 the thorax or abdomen, respiratory rhythm becomes more frequent 

 and superficial. 



Where there is morbid stenosis of the air-passages, the respira- 

 tions become deeper and less frequent. In pneumonia or pleurisy, 



