RESPIRATION. 563 



In snoring the mouth is open, and the inflow and outflow of air throws the 

 uvula and the soft palate into vibration. The sound produced is more marked 

 during inspiration, and may even be absent during expiration. It is more apt 

 to occur when the individual is lying on his back than when in any other 

 posture. Snoring is usually involuntary, but it may be volitional. 



In gargling the fluid is held between the tongue and the soft palate and air 

 is expired through it in the form of bubbles. 



In hiccough there is a sudden inspiratory effort caused by a spasmodic 

 twitch of the diaphragm and attended by a sudden closure of the glottis, so 

 that the inspiratory movement is suddenly arrested, thus causing a characteris- 

 tic sound. Hiccough is sometimes not only distressing, but may be even seri- 

 ous or fatal in its consequences. It is especially apt to occur in cases of gastric 

 irritation, in certain forms of hysteria, in alcoholism, in uraemia, etc. 



Besides the above special respiratory movements, others are observed in 

 certain species of animals, such as whining, neighing, braying, roaring, bellow- 

 ing, bawling, barking, purring, growling, etc. 



Of all these modified respiratory movements, coughing possesses to the 

 clinician the most interest, because it not only may express an abnormal condi- 

 tion of some portion of the lungs, trachea, or larynx, but may indicate irrita- 

 tion in even remote and entirely unassociated parts. Thus, coughing may be 

 the result of irritation in the nose, ear, pharynx, stomach, liver, spleen, intes- 

 tines, ovaries, testicle, uterus, or mamma. Coughs which are not dependent 

 upon irritation of the larynx, trachea, or lungs are distinguished as sympa- 

 thetic or reflex coughs. The term " reflex " is a bad one, however, inasmuch 

 as all coughs are essentially or solely reflex. 



K. THE NERVOUS MECHANISM OF THE RESPIRATORY MOVEMENTS. 



The movements of respiration are carried on involuntarily and automati- 

 cally that is, they recur by virtue of the activity of a self-governing mech- 

 anism. Each respiratory act necessitates a finely co-ordinated adjustment of 

 the contractions of a number of muscles, which adjustment is dependent upon 

 the operations of a dominating or controlling nerve-centre located in the 

 medulla oblongata, and known as the respiratory centre. Besides this centre, 

 others of minor importance have been asserted to exist in certain parts of the 

 cerebro-spinal axis ; these centres are distinguished as subsidiary or subordinate 

 respiratory centres. Connected with the respiratory centre are afferent and 

 efferent respiratory nerves. 



The Respiratory Centres. After removal of all parts of the brain except 

 the spinal bulb, rhythmical respiratory movements may still continue, but after 

 destruction of the lower part of the bulb they at once cease. These facts indi- 

 cate that the centre for these movements is in the medulla oblongata, and this 

 conclusion is substantiated by the results of other experiments upon this 

 region. According to the observations of Flourens, the respiratory centre is 

 located in an area about 5 millimeters wide between the nuclei of the pneumo- 

 gastric and spinal accessory nerves in the lower end of the calamus scriptorius. 



