84 NERVOUS SYSTEM. 



4. In artificial respiration the rhythmical action of the laryngeal and facial 

 muscles continues, and follows the rhythm of the artificial respirations, each 

 injection of air being followed by expiratory movements of the nares and 

 glottis. 5. Excitation of the central end of the divided sup. laryng. nerve 

 always produces transitory cessation of respiratoiy movements with relaxed 

 diaphragm. The same effect is produced by injection of air impregnated 

 with NH 3 gas into the larynx from below. 6. Excitation of the central end 

 of the divided vagus produces sometimes continuous or interrupted contraction 

 of the diaphragm, sometimes the effects described in 5. 7. Respiration of an 

 atmosphere containing excess of CO 2 (20% or more) does not produce 

 dyspnoea if as much as 2O C / of O be present. 8. Dyspnoea is produced by 

 warming the blood which is supplied to the medulla oblongata, whether the 

 general temperature of the body be raised or not. 



Reflex respiratory movements. Co-ordinated respiratory 

 movements adapted for the exclusion or expulsion of 

 irritating substances from the respiratory cavities, are 

 determined either by mechanical or chemical excitation 

 of the nares (sneeze), of the mucous membrane below 

 and on either side of the epiglottis (closure of the glottis), 

 or of the vocal cords (cough), or of the bronchial mucous 

 membrane (paroxysm of cough by summation). In 

 coughing and sneezing, each reflex effect consists of three 

 acts, viz., a short inspiration, followed by a violent expul- 

 sive burst of air through a previously closed air-way, in 

 the production of which all the expiratory muscles, both 

 the constrictors of the abdominal cavity, and the depres- 

 sors of the lower ribs, take part. The closure, which is 

 the second phase in the process, takes place in cough at 

 the glottis, in the sneeze at the fauces. The afferent 

 channels concerned in these reflexes are contained in the 

 middle division of the trigeminus and the vagus. The 

 muscles are those of respiration and of the fauces and 

 soft palate. 



The various abnormal modes of respiration which occur in disease, may be 

 referred either to altered rhythm of the centre (Cheyne Stokes breathing), to 

 excessive proneness to the production of reflex expiratory action (spasmodic 

 cough), to suspension of vagus action (true asthma), &c. 



Influence of the Nervous System on the Heart. i. The 



