CONDITIONS ACTING ON THE RESPIRATORY CENTRE. 



665 



C0 2 given off, however, is unchanged, but the inspiratory efforts are more vigorous 

 and not so purposive (Gad). Weak tetanising currents applied to the central end 

 of the vagus, cause acceleration of the respirations, while, at the same time, the 

 efforts of the respiratory muscles may be increased, or diminished, or remain un- 

 changed (Gad). Strong tetanising currents cause standstill of the respiration in 

 the inspiratory phase (Traube), or especially in fatigue of the nerves, in the 

 expiratory phase (Budge, Burkart). Single induction shocks have no effect 

 (Marckwald and Kronecker). 



[Marckwald, while admitting that the respiratory centre is automatically active, as well as 

 capable of being affected reflexly, comes to the conclusion, that, when the centre is 

 separated from all nerve-channels by which afferent impulses can be conveyed to it, it is 

 incapable of discharging rhythmical respiratory movements. He also asserts that the normal 

 rhythmical respiration is a reflex act discharged chiefly through the vagi, and that the normal 

 excitant of the respiratory centre is not dependent on the condition of the blood, either on the 

 diminution of 0, or the increase of C0 2 . These results are opposed to the usually accepted 

 view, and they are controverted by Loewy. Division of the medulla oblongata above the 

 respiratory centre, so as to cut off all cerebral channels of communication, has very little 

 effect on the respirations. If, after this, one, or both vagi be divided, there is (1) an extra- 

 ordinary slowing of the respiration ; the number of respirations may fall in the rabbit, from 

 20 to 2 or 4 per minute ; (2) the rhythm is changed, in some cases the inspiration may be 

 twice or thrice as long as the expiration, but, whatever the ratio of inspiration to expiration, 

 the respiration is rhythmical ; (3) the volume of air respired is diminished (p. 664), but the 

 volume for each respiration is deeper; (4) the intra-thoracic pressure is increased, during 

 inspiration, and during expiration it is the same as before the vagotomy.] 



[The above table (from Loewy) shows the result. Loewy finds that, if the centre be separated 

 from all centripetal channels, it still discharges respiratory movements, which are rhythmical, 

 and he has shown that these rhythmical discharges are due to the condition of the blood.] 



[If one lung be made atelectic, i.e., devoid of air, e.g., by plugging its bronchus with a 

 sponge-tent, then the pulmonary fibres of the vagus from this lung are no longer excited during 

 respiration, and their section has no effect on the respiration. Section of the vagus on the 

 sound side, however, has the same consequence as double vagotomy {Loewy). 1 



Wedenski and Heidenhain find that a temporary, weak, electrical stimulus applied to the 

 central end of the vagus, at the beginning of inspiration (rabbit), affects the depth of the 

 succeeding inspirations, while a similar strong stimulus affects also the depth of the following 

 expirations. If the stimulus be applied just at the commencement of expiration, stronger 

 stimuli being required in this case, there is a diminution of the expiration and of the following 

 inspiration. Continued tetanic stimulation of the vagus may cause decrease in the depth of 

 the expirations, or at the same time alteration in the depth of the inspirations, without 

 affecting the respiratoiy rhythm ; when the stimulation is stronger, inspiration and expiration 

 are diminished with or without alteration of the frequency, and with the strongest stimuli, 

 respirations cease either in the inspiratory or expiratory phase. 



(b) The inhibitory nerves which affect the respiratory centre run in the superior 

 laryngeal nerve (Rosenthal), and also in the inferior (Pflikjer and Burkart, Hering, 

 Breuer), to the respiratory centre (fig. 467, inh). 



According to Langendorff, direct electrical, mechanical, or chemical stimulation of the centre 

 may arrest respiration, perhaps in consequence of the stimulus affecting the central ends of 

 these inhibitory nerves where they enter the ganglia of the respiratory centre. During the 

 reflex inhibition of the respiration in the expiratory phase, there is a suppression of the motor 

 impulse in the inspiratory centre ( Wegete). 



Stimulation of the superior or inferior laryngeal nerves (b) or their central ends 



