INFLUENCE OF NEKVES ON RESPIRATION. 817 



to others, it is rather the want of oxygen, which excites the movements, 

 for an excess of that element enfeebles them. 



The division of one vagus nerve in an animal, as a rule, lowers the 

 frequency of, and embarrasses, the respiration, and the lungs become 

 sometimes, but not always, the seat of extravasations of blood. Divis- 

 ion of both vagi nerves in the neck immediately diminishes the frequency 

 of the respirations to one-half, and later to one-third, or even one- 

 fourth, of the normal number; the inspirations become not only slower, 

 but deeper, embarrassed, and puffing, or spasmodic ; the expirations, on 

 the other hand, are shorter; whilst the pause between the expiration 

 and the succeeding inspiration becomes more and more prolonged, 

 which accounts for the diminished number of respiratory acts in a given 

 time. Death usually takes place after from two to six days; the blood 

 first becomes darker, as indicated by blueness of the lips, the tempera- 

 ture sinks, and the animal dies of asphyxia. Congestion of the pul- 

 monary vessels, extravasations of blood, and exudations of frothy san- 

 guineous serum and mucus, are found in the air-cells and bronchial 

 tubes, and partial solidification of the lung-tissue occurs. Sometimes, 

 however, death appears to ensue from disturbance of the digestive 

 functions; but if these be recovered from, the animals may then live 

 for many days. The continuance of the respiratory movements, for a 

 time, after division of the pneumogastric nerves, depends on the ex- 

 citability of the other afferent nerves of the body, especially of those 

 of the skin. It seems doubtful whether the unstriped muscular fibres 

 of the bronchial tubes can be excited through the pneumogastric 

 nerves. Their contractility is soon exhausted by stimuli directly ap- 

 plied to them ; moreover, it is lessened by certain narcotics, especially 

 by belladonna and stramonium ; hence the use of such remedies in 

 asthma, in relieving the paroxysms of dyspnoea, which are supposed 

 to be due to a spasmodic contraction of these organic muscular fibres. 



The respiratory apparatus is employed, either voluntarily or invol- 

 untarily, in many other acts necessary to the economy, or conducive 

 to its comfort. In these, the movements of respiration are sometimes 

 accelerated or strengthened, and sometimes diminished or checked. 



Thus, speaking, singing, shouting, and whistling, are volitional 

 movements, requiring special voluntary efforts of expiration, often 

 modified and graduated in the most varied yet exact manner, and sup- 

 ported by inspirations performed at stated and suitable times. The 

 act of spitting consists of a sudden expiration accompanied by a pecu- 

 liar position of the tongue, lips, teeth, and cheeks, having for its object 

 the expulsion of saliva or other accumulations from the mouth. 



The semi-voluntary or involuntary acts which necessitate the co-op- 

 eration of the respiratory apparatus, are much more varied. Thus, 

 coughing is a sudden, strong expiration, accompanied by a peculiar 

 noise, following a closure of the glottis and of the upper opening of the 

 larynx, and usually preceded by a deep inspiration, to give effect to 

 the cough. A column of air, suddenly driven from the air-tubes, as 

 suddenly opens the glottis, and, being forced through the mouth,, moves 

 on accumulations or foreign bodies, and expels them from the bronchi, 



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