MODIFIED RESPIRATORY MOVEMENTS. 403 



whose store of haemoglobin in proportion to their body weight is always 

 below par, are proverbially " scant of breath." 



MODIFIED KESPIRATORY MOVEMENTS. 



334. The respiratory mechanism with its adjuncts, in addition to its 

 respiratory function, becomes of service, especially in the case of man, as a 

 means of expressing emotions. The respiratory column of air, moreover, in 

 its exit from the chest, is frequently made use of in a mechanical way to 

 expel bodies from the upper air-passages. Hence arise a number of pecu- 

 liarly modified and more or less complicated respiratory movements, sighing, 

 coughing, laughter, etc., adapted to secure special ends which are not dis- 

 tinctly respiratory. They are all essentially reflex in character, the stimulus 

 determining each movement, sometimes affecting a peripheral afferent nerve 

 as in the case of coughing, sometimes working through the higher parts of 

 the brain as in laughter arid crying, sometimes possibly as in yawning and 

 sighing, acting on the respiratory centre itself. Like the simple respiratory 

 act, they may with more or less success be carried out by a direct effort of 

 the will. 



Sighing is a deep and long-drawn inspiration, chiefly through the nose, 

 followed by a somewhat shorter, but correspondingly large expiration. 



Yawning is similarly a deep inspiration, deeper and longer continued 

 than a sigh, drawn through the widely open mouth, and accompanied by a 

 peculiar depression of the lower jaw and frequently by an elevation of the 

 shoulders. 



Hiccough consists in a sudden inspiratory contraction of the diaphragm, 

 in the course of which the glottis suddenly closes, so that the further entrance 

 of air into the chest is prevented, while the impulse of the column of air 

 just entering, as it strikes upon the closed glottis, gives rise to a well-known 

 accompanying sound. The afferent impulses of the reflex act are conveyed 

 by the gastric branches of the vagus. The closure of the glottis is carried 

 out by means of the inferior laryngeal nerve. See Voice. 



In sobbing a series of similar convulsive inspirations follow each other 

 slowly, the glottis being closed earlier than in the case of hiccough, so that 

 little or no air enters into the chest. 



Coughing consists in the first place of a deep and long-drawn inspiration 

 by which the lungs are well filled with air. This is followed by a complete 

 closure of the glottis, and then comes a sudden and forcible expiration, in 

 the midst of which the glottis suddenly opens, and thus a blast of air is 

 driven through the upper respiratory passages. The afferent impulses of 

 this reflex act are, in most cases, as when a foreign body is lodged in the 

 larynx or by the side of the epiglottis, conveyed by the superior laryngeal 

 nerve ; but the movement may arise from stimuli applied to other afferent 

 branches of the vagus, such as those supplying the bronchial passages and 

 stomach and the auricular branch distributed to the meatus extefnus. Stimu- 

 lation of other nerves also, such as those of the skin by a draught of cold 

 air, may develop a cough. ' 



In sneezing the general movement is essentially the same, except that the 

 opening from the pharynx into the mouth is closed by the contraction of the 

 anterior pillars of the fauces and the descent of the soft palate, so that the 

 force of the blast is driven entirely through the nose. The afferent impulses 

 here usually come from the nasal branches of the fifth. When sneezing, 

 however, is produced by a bright light, the optic nerve would seem to be the 

 afferent nerve. 



Laughing consists essentially in an inspiration succeeded, not by one, but 



