274 



RESPIRATION 



cough, which may also be caused by irritation of the pulmonary 

 fibres of the vagus. 



Action of Other Afferent Fibres on the Respiration. The cutaneous 

 nerves, and especially those of the face (fifth nerve), abdomen and 

 chest, have a marked influence on respiration. They can be easily 

 excited in the intact body by thermal and mechanical stimulation. 

 A cold bath, for instance, usually causes acceleration and deepening 

 of the respiratory movements ; and the efficacy of mechanical stimu- 

 lation of sensory nerves in stirring up a sluggish respiratory centre 

 is well known to midwives, who sometimes slap the buttocks of a new- 



Fig. 126. Effect of Stimulation of Central End of Brachial Nerve on Respiration 

 (Upper Tracing) and Blood-Pressure (Lower Tracing) in the Cat. At the top of 

 the figure are the time-trace (seconds) and the signal line, showing beginning and 

 end of stimulation. 



born child to start its breathing. The reflex expiratory standstill 

 caused in rabbits by inhalation of such sharp-smelling substances as 

 ammonia, acetic acid, and tobacco-smoke is due to afferent impulses 

 passing up the trigeminus fibres from the mucous membrane of the 

 nose, and is still obtained after section of the olfactory nerves. 



Another set of afferent nerves which have been supposed by some 

 to bear an important relation to the respiratory centre are those 

 which supply the muscles. We have already noticed that the 

 frequency of respiration is greatly augmented by muscular exercise. 

 The simplest explanation would seem to be that afferent muscular 

 nerves are stimulated either by mechanical compression of their 



