452 Disturbances of Respiration. 



clonic convulsions occur and death follows after a short period of 

 paralysis (Krehl). Where the irritability of the central nervous 

 system is diminished (haemorrhages into the brain, increased 

 intracranial pressure, toxic or infectious influences) the symptoms 

 caused by diminution in oxygen supply are less violent; the 

 gradual and progressive increase of carbon dioxide produces a 

 cerebral narcosis, the respiratory movements become gradually 

 weaker and life ebbs away with the advancing paralysis of the 

 central nervous organs (Krehl). 



The respiratory tubes are provided with a number of pro- 

 tective mechanisms, which serve to remove foreign particles 

 which have gotten into the air passages. The. passage to the 

 trachea and lungs leads over an area, the naso-pharynx, richly 

 inhabited by bacteria and often the point of lodgment of foreign 

 bodies; the narrow laryngeal opening is the threshold separating 

 this septic territory from the tracheal system. Of course, the 

 larger foreign particles which get into the nose and pharynx 

 and which irritate the nerves of the mucous surface and thus in- 

 duce sneezing and snorting, are from time to time discharged, 

 and the entrances for air are kept free for the passage of air; 

 but motile virulent organisms may easily pass in, and aspiration 

 of small drops of septic mucus and saliva or even food particles 

 may readily occur. In this case (these substances having passed 

 into the trachea and bronchi) the continued activity of the ciUated 

 cells serves to remove these foreign particles, carrying them back 

 to the trachea and larynx. The mucus secreted over the whole 

 surface of the tubes serves to envelop the foreign elements, and, 

 too, dilutes the poisonous substances and renders them inert. 

 Moreover, the numerous depots of lymphoid cells may make an 

 efficient phagocytosis possible and thus facilitate the removal of 

 very minute foreign particles. In addition the reflex production 

 of coughing, which forcibly discharges foreign objects, the col- 

 lections of mucus to which they are adherent and any other 

 injurious contents of the trachea, is manifested and acts to cleanse 

 the upper portion of the tubes. Excitation of cough is prin- 

 cipally induced by local irritation of the sensor}^ vagus fibres in 

 the larynx and trachea, and may also originate in the pleura, a 

 special group of movements of the respiratory muscles being ex- 

 cited reflexly through the medulla oblongata. Cough begins with 

 a deep inspiration, followed by a forcible expiration ; the air under 

 high pressure in the lungs forces its way out through the opening 



