CH. XXIV.] CHEYNE-STOKES BREATHING 365 



and the point of bifurcation of the trachea is specially sensitive. 

 Other sensory surfaces may also act as the "signal surface" for a 

 cough. Thus, a cold draught on the skin, or tickling the external 

 auditory meatus, in some people will set up a cough. 



The question has been discussed whether such a thing as a stomach 

 cough exists ; it has not been produced experimentally, but there is no 

 reason why irritation of the gastric mucous membrane, supplied as it 

 is by the vagus, should not cause the reflex act of coughing. 



Sneezing. The same remarks that apply to coughing are almost 

 exactly applicable to the act of sneezing; but, in this instance, the 

 blast of air, on escaping from the lungs, is directed, by an instinctive 

 contraction of the pillars of the fauces and descent of the soft palate, 

 chiefly through the nose, and any offending matter is thence expelled. 



The " signal surface " is usually the nasal mucous membrane, but 

 here, as in coughing, other causes (such as a bright light) will some- 

 times set the reflex going. 



Hiccough is an involuntary sudden contraction of the diaphragm, 

 causing an inspiration which is suddenly arrested by the closure of 



FIG. 332. Cheyne-Stokes respiration. (After Waller.) 



the glottis, causing a characteristic sound. It arises from gastric 

 irritation. 



Snoring is due to vibration of the soft palate. 



Sobbing consists of a series of convulsive inspirations at the moment 

 of which the glottis is partially closed. 



Sighing and Yawning are emotional forms of inspiration, the latter 

 associated with stretching movements of jaws and limbs. They appear 

 to be efforts of nature to correct, by an extra deep inspiration, the 

 venosity of the blood due to inactivity produced by ennui or grief. 

 Their contagious character is due to sympathy. 



Among abnormal disturbances of the nervous mechanism of 

 respiration, the following diseases must be mentioned: laryngismus 

 stridulus, asthma, and whooping-cough. 



Cheyne-Stokes respiration is due to rhythmical activity of the 

 respiratory centre. It reminds one somewhat of the Traube-Hering 

 waves due to a similar rhythmical activity of the vaso-motor centre. 

 It is seen in many nervous diseases and in fatty degeneration of the 

 heart. A typical tracing of the condition is given above (fig. 332). 

 It is seen to a slight extent during ordinary sleep, and is very marked 

 in hibernating animals. 



