438 PHYSIOLOGY CHAP. 



with effusions into the pleural cavity, both frequency and depth 

 of rhythm are accentuated. 



Both secretions and exudations along the air-passages, as also 

 foreign bodies, solid, liquid, or gaseous, which penetrate them, 

 readily produce a reflex cough. This consists in loud, expiratory 

 efforts, which produce enforced opening of the previously closed 

 glottis, and by means of which the irritant is expelled. Coughing 

 may be voluntary, and even when the cough is involuntary, it can 

 be moderated and even inhibited by the will. 



The presence of mucus, of foreign bodies, or of substances which 

 irritate the nasal mucosa, may give rise to sneezing, which consists 

 in one or more sudden and noisy expirations through the nasal 

 passages, preceded by profound inspirations. In sneezing, the 

 glottis is always open, the posterior nares are constricted by the 

 rise of the soft palate, the mouth is seldom open. It is invariably 

 a reflex act, which can only be imitated imperfectly by the will ; 

 it can, however, be voluntarily modified. The use of snuff makes 

 the nasal mucosa insensitive after a few days, and suppresses 

 sneezing. 



Noisy crying, such as is frequent in childhood and youth, as 

 the expression of physical and moral pain, consists in short and 

 spasmodic inspirations, followed by prolonged expirations, with 

 constricted glottis, relaxed muscles of face and jaw, simultaneous 

 flow of tears and emission of high, inarticulate, laryngeal sounds. 

 Sometimes it is associated with sobbing, which consists in repeated 

 contractions of the diaphragm, producing sudden closure of the 

 vocal cords, with a characteristic and quite involuntary sound. 



Noisy laughter, the expression of sudden pleasant and un- 

 expected sensations, or of hysteria, consists in short and rapidly 

 succeeding expiratory efforts through the vocal cords, which are 

 now brought close, and now separated, producing high, clear, and 

 inarticulate tones, with trembling of the soft palate. The mouth 

 is generally open, and the facial muscles contract in a characteristic 

 manner. Laughter can easily be imitated at will, and to a certain 

 extent can be voluntarily suppressed or moderated. 



Yawning, the external expression of ennui, drowsiness, hunger, 

 consists in a long, deep inspiration, in which many of the accessory 

 inspiratory muscles participate, while the mouth, fauces, and 

 glottis open convulsively. Inspiration is followed by a shorter 

 expiration, and the two acts are accompanied by prolonged 

 characteristic sounds, and by a general stretching of the arms and 

 trunk. It is always an involuntary modification of breathing, 

 easily imitated by the will. 



