NERVOUS MECHANISM OF RESPIRATION 169 



spiration exciting expiratory fibers, and movements of ex- 

 piration exciting inspiratory -fibers. These observers cite 

 the fact that artificial inflation and aspiration excite expira- 

 tion and inspiration respectively. 



Stimulation of the superior laryngeal, as when foreign 

 bodies accidentally enter the larynx, excites violent expira- 

 tion. 



The glosso-pharyngeal contains afferent fibers especially 

 important in arresting respiration at any stage whatever 

 during the act of deglutition. 



Stimulation of the sensory fibers of the trigeminal in the 

 nose, as by irritating vapors, may arrest respiration. 



Irritation of the cutaneous nerves in general, as by cold or 

 hot water, slapping, etc., stimulates respiratory movement. 



There are, of course, running from the cortex to the res- 

 piratory center intracranial fibers whereby the organ of the 

 will makes its presence felt in respiration. 



But when all the afferent nerve connections are severed, 

 respiration continues with modified rhythm and rate, at least 

 for a time. It is thought that, under these conditions, it is 

 the circulation through the center of blood deficient in oxy- 

 gen which causes the cells to discharge ; that is, after every 

 inspiration and subsequent expiration there is not another 

 inspiration until the blood has become sufficiently deoxygen- 

 ated, or charged with carbon dioxide, to irritate the respira- 

 tory center. 



We may conclude that "the rhythmical discharges from 

 the center are due primarily to an inherent quality of peri- 

 odic activity of the nerve cells constituting the respiratory 

 center, and maintained by the blood, and that the rhythm, 

 rate, and other characters of these discharges may be af- 

 fected by the will and the emotions, by the composition, sup- 

 ply and temperature of the blood, and by various afferent im- 

 pulses. The chief factors are the quantities of O and 

 CO2 in the blood, and the impulses conveyed from the lungs 

 by the fibers of the pneumogastric nerves." (Am. Text- 

 .Book.) 



