RESPIRATION 125 



involve the respiratory mechanism more than that of any other func- 

 tional system. These are, among others, speaking, singing, coughing, 

 sneezing, hawking, sniffing, yawning, sighing, laughing, sobbing, snoring, 

 sucking, and hiccoughing, thirteen functions less formidable to under- 

 stand than one might fear. The first two are so important and complex 

 that they require special discussion in the proper place immediately 

 below. The next four coughing, sneezing, hawking, and sniffing are 

 movements habitual to many mammals for the purpose of clearing the 

 respiratory passages of mucus and other obstructions and irritants. 

 The next one yawning is a mode of muscular relief. The next 

 three sighing, laughing, and sobbing are emotional expressions. The 

 general nature and the purpose of the next sucking and snoring are 

 known to everyone. Hiccoughing alone seems to be strictly abnormal. 

 Here we need discuss only two of these processes. 



Coughing is an essentially protective process in catarrhal inflamma- 

 tion of the respiratory passages and useful for removing from them 

 accidental particles, as of food. When both vagus nerves are cut in the 

 neck, the afferent impulses to coughing are cut off, and the animal 

 usually dies in a few weeks or months from foreign-body pneumonia. 

 Coughing may be either a voluntary action or one reflexly started. 

 It consists first of a very deep and full inspiration, with the closure 

 of the glottis, followed by a forced expiration. When the increasing 

 pressure in the larynx is sufficient the glottis is burst open and the 

 current of air passing violently out through the previously opened mouth 

 tends to remove the irritating substances. Stirling enumerates eight 

 sources of stimulation of reflexly produced coughs: (1) The respiratory 

 mucous membrane, especially of the larynx, the afferent impulses of the 

 reflex arc going in over the vagus and the superior laryngeal. Kohts 

 determined that a cough-stimulus could come from only the glottis res- 

 piratoria, not from the true vocal cords nor from the trachea down to the 

 bifurcation. (2) The skin, especially of the upper part of the body, a 

 cold draught on which produces a congestion of the air-passages, which 

 in turn excites coughing. (3) The external auditory meatus, where a 

 foreign body may start impulses inward over the auricular branch of 

 the vagus. (4) The mucosa of the stomach, the afferent nerves being 

 again in the vagus. (5) The costal pleura and (Kohts) the esophagus. 

 (6) The nose. (7) The pharynx. (8) The liver, spleen, and generative 

 organs in diseased condition when pressure is applied over them. 



Sneezing is similar to coughing save that the blast of air from the 

 trachea passes out through the nose instead of the mouth, the latter being 

 tightly closed. Sneezing is much more reflex than is coughing. A bright 

 light even may occasion a sneeze. The remainder of these subsidiary 

 respiratory processes are of interest, but do not need special description. 



The Respiratory Sounds. As might be expected in a process where 

 currents of air rush in and out through a series of tubes and chambers 

 more or less obstructed in various ways, the function of respiration is 

 accompanied by various sounds. These are audible either by the unaided 



