xin RESPIRATORY RHYTHM 465 



produces a retarded respiration, with prolonged expiratory pauses. 

 With a stronger stimulus the expirations become very vigorous, 

 and assume the form of expiratory tetanus (Rosenthal). 



The effects of stimulating the glosso - pharyngeal are less 

 constant. Apparently this determines respiratory standstill in 

 the phase of the respiration that obtained prior to excitation. 

 Few experiments, however, have been made on this point. 



In any case these afferent nerve fibres, situated along the 

 air-passages, which when stimulated have a moderating action 

 on the respiratory processes, or a decisively active expiratory 

 influence, do not function under ordinary conditions of lite, since 

 they have normally no tonicity, and are not therefore capable, 

 like the pulmonary fibres of the vagus, of exerting a constant 

 influence upon the bulbar centres. Cocainisation of the nasal 

 mucosa (Marckwald), and bilateral intracranial section of the 

 trigeminus (Loewy), effect no permanent alteration in respiratory 

 rhythm. On a rabbit operated on in this way successive vagotomy 

 produces no more pronounced effect than when the operation is 

 performed on an intact rabbit. The paths of the trigeminus do 

 not, therefore, normally exert any regulatory control upon the 

 respiratory impulses sent out from the centres. 



The same may be affirmed of the afferent paths of the glosso- 

 pharyngeal and superior and inferior laryngeals, section of which 

 produces no permanent modification of respiratory rhythm. 



All other centripetal paths, which lead directly or indirectly, 

 from above or from below, to the respiratory centres, and which 

 under normal conditions do not influence the respiratory mechanism, 

 may, when artificially excited, or under certain fortuitous conditions, 

 produce modifications in respiration. 



Stimulation of the olfactory nerve by odoriferous substances 

 may give rise now to inspiratory and now to expiratory effects, 

 according to the acuteness of the sensations evoked, and their 

 pleasant or unpleasant character. Electrical excitation of the 

 optic and auditory nerves regularly produces acceleration of 

 rhythm, with reinforcement of inspirations. The sensory 

 nerves to the skin, when slightly stimulated, excite inspiratory 

 effects ; with painful stimulation, they exaggerate and prolong the 

 expiratory acts. The phrenic nerves also contain afferent fibres, 

 which when excited behave like the cutaneous nerves. So, too, the 

 centripetal nerves of the sympathetic system are able reflexly to 

 modify respiratory rhythm. According to Pfliiger, excitation of 

 the splanchnic invariably produces respiratory effects, which do not 

 occur on exciting other rami of the sympathetic. 



The majority of these reflexes are of no essential importance 

 to the theory of the nervous mechanisms that normally and 

 continuously regulate the respiratory rhythm. On the other 

 hand, a special importance in the auto-regulation of respirations 



VOL. I 2 H 



