378 PHYSIOLOGY. 



tion, since it is purely reflex; a person usually will not yawn if the 

 need of doing it does not exist. Besides its relation to oxidation, it 

 also expresses painful sensations in the stomach, hunger, or a feeling 

 of torpor at the approach of sleep. 



THE HICCOUGH cannot be compared with the acts connected with 

 respiration, except by the noise accompanying it. It is a spasmodic 

 contraction, abrupt and involuntary, of the diaphragm with coincident 

 contraction of the glottis. The air, drawn rapidly into the chest by 

 the convulsive contraction of the diaphragm, breaks upon the out- 

 stretched lips of the glottis, where is produced the sound characteris- 

 tic of hiccough. The ordinary causes for this phenomena are en- 

 gendered in the stomach by the too rapid introduction of alimentary 

 substances, by alcoholic drinks and by nervous disturbances. 



COUGHING usually arises from an irritation in the laryngeal pas- 

 sage; the irritating effect of the sensory filaments of the larynx 

 reaches a certain intensity; there is then a deep inspiration, which is 

 followed by a sudden and strong expiration. 



Coughing can be produced voluntarily, but it is more often 

 caused by reflex action, which it is generally impossible to resist. A 

 cold draught on the skin or a tickling of the external auditory meatus 

 will provoke a cough in some people. 



LAUGHING AND SOBBING have this feature in common : they have 

 their seat in the chest and face at the same time. They act especially 

 upon the same muscle : the diaphragm. In the face they differ in 

 this, that one has its own particular seat in the region of the eye, the 

 other around the mouth. The same muscles, the same nerves, pro- 

 duce sobs and laughter. Their movements of inspiration and expira- 

 tion are, however, accompanied by their own characteristic sounds. 



SNORING is due to vibration of the soft palate. 



CHEYNE-STOKES EESPIRATION. This is a peculiar modification 

 of the respiratory movements which is seen in certain pathological 

 conditions, as in fatty heart, atheroma of the aorta, certain apoplex- 

 ies, and in uraemia. It has even been noted in healthy children dur- 

 ing sleep. It consists of respiratory pauses alternating with a series 

 of respirations till a maximum depth and rapidity is reached; after 

 this climax they gradually diminish till they end in another pause. 

 Certain drugs chloral is one may cause Cheyne-Stokes respiration. 



Cheyne- Stokes respiration rhythm is to the respiratory center 

 what the Traube-Hering rhythm is to the vasomotor center. Both 

 arise in their respective centers in the medulla oblongata. 



