CHEMISTRY OF RESPIRATION. 1 83 



but only from the glottis respiratoria. All other parts of the larynx are inactive, and so is the 

 trachea as far as the bifurcation, where stimulation excites cough (Kohts). (3) Sometimes an 

 offending body, such as a pea or inspissated cerumen in the external auditory meatus, gives rise 

 to coughing, the afferent nerve being the auricular branch of the vagus. (4) There seems to be 

 no doubt that there may be a " gastric or stomach cough," produced by stimulation of the gastric 

 branches of the vagus, especially in cases of indigestion, accompanied by irritation of the larynx 

 and trachea. (5) Irritation of the costal pleura and even of the oesophagus (Kohts). (6) Irrita- 

 tion of some parts of the nose. (7) Sometimes also from irritation of the pharynx, as by an 

 elongated uvula. (8) In some diseases of the liver, spleen, and generative organs, when pressure 

 is exerted on these parts. ] 



(2) Hawking, or clearing the throat. An expiratory current is forced in a continuous stream 

 through the narrow space between the root of the tongue and the depressed soft palate, in order 

 to assist in the removal of foreign bodies. When the act is carried out periodically, the closed 

 glottis is suddenly forced open, and it is comparable to a voluntary gentle cough. This act can 

 only be produced voluntarily. 



(3) Sneezing consists in a sudden violent expiratory blast through the nose, for the removal 

 of mucus or foreign bodies (the mouth being rarely open) after a simple or repeated spasm-like 

 inspiration the glottis remaining open. It is usually caused refiexly by stimulation of sensory 

 nerve-fibres of the nose [nasal branch of the fifth nerve], or by sudden exposure to a bright light 

 [the afferent nerve is the optic]. This reflex act may be interfered with to a certain extent, or 

 even prevented, by stimulation of sensory nerves, or firmly compressing the nose where the 

 nasal nerve issues. The continued use of sternutatories, as in persons who take snuff, dulls the 

 sensory nerves, so that they no longer act when stimulated refiexly. 



[Sternutatories or Errhines, such as powered ipecacuanha, snuff, and euphorbium, also in- 

 crease the secretion from the nasal glands. The afferent impulses sent to the respiratory centre 

 also affect the vaso-motor centre, so that, even when sneezing does not occur, the blood-pressure 

 throughout the body is raised.] 



(4) Snoring occurs during respiration through the open mouth, whereby the inspiratory and 

 expiratory stream of air throws the uvula and soft palate into vibration. It is involuntary, and 

 usually occurs during sleep, but it may be produced voluntarily. 



(5) Gargling consists in the slow passage of the expiratory air-current in the form of bubbles 

 through a fluid lying between the tongue and the soft palate, when the head is held backwards. 

 It is a voluntary act. 



(6) Crying, caused by emotional conditions, consists in short, deep inspirations, long expira- 

 tions with the glottis narrowed, relaxed facial and jaw muscles, secretion of tears, often com- 

 bined with plaintive inarticulate expressions. When crying is long continued, sudden and 

 spasmodic involuntary contractions of the diaphragm occur, which cause the inspiratory sounds 

 in the pharynx and larynx known as sobbing. This is an involuntary act. 



(7) Sighing is a prolonged inspiration, usually combined with a plaintive sound, often caused 

 involuntarily, owing to painful or unpleasant recollections. 



(8) Laughing is due to short rapid expiratory blasts through the tense vocal cords, which 

 cause a clear tone, and there are characteristic inarticulate sounds in the larynx, with vibra- 

 tions of the soft palate. The mouth is usually open, and the countenance has a characteristic 

 expression, owing to the action of the M. zygomaticus major. It is usually involuntary, and 

 can only be suppressed, to a certain degree, by the will (by forcibly closing the mouth and 

 stopping respiration). 



(9) Yawning is a prolonged deep inspiration occurring after successive attempts at numerous 

 inspirations the mouth, fauces, and glottis being wide open; expiration shorter both acts 

 often accompanied by prolonged characteristic sounds. It is quite involuntary, and is usually 

 excited by drowsiness or ennui. 



[(10) Hiccough is due to a spasmodic involuntary contraction of the diaphragm, causing an 

 inspiration, which is arrested by the sudden closure of the glottis, so that a characteristic sound 

 is emitted. Not unfrequently it is due to irritation of the gastric mucous membrane, and some- 

 times it is a very troublesome symptom in urcemic poisoning.] 



121. CHEMISTRY OF RESPIRATION CARBON DIOXIDE, OXYGEN, and WATERY 

 VAPOUR GIVEN OFF. I. Estimation of C0 2 . 1. The volume of C0 2 is estimated by means 

 of the anthracometer (fig. 143, II). The volume of gas js collected in a graduated tube, rr, 

 provided with a bulb at one end (previously filled with water and carefully calibrated, i.e., the 

 exact amount which each part of the tube contains is accurately measured), and the tube is closed. 

 The lower end has a stop-cock, h, and to this is screwed a flask, n, completely filled with a solu- 

 tion of caustic potash ; the stop-cock is then opened, the potash solution is allowed to ascend 

 into the tube, which is moved about until ail the C0 2 unites with the potash to form potassium 

 carbonate. Hold the tube vertically and allow the potash to run back into the flask, close the 

 stop-cock, and remove the bottle with the potash. Place the stop-cock under water, open it, and 

 allow the water to ascend in the tube, when the space in the tube occupied by the fluid indicates 

 the volume of C0 2 which is combined with the potash. 



