XIII 



KESPIBATOKY EHYTHM 



485 



return to normal respiration at the close of insufflation is 

 invariably preceded by an increase in the respiratory movements 

 (Fig. 219). 



(&) In pigeons also the apnoea is constant. At a pressure of 

 1-2 mm. Hg expiratory arrest is instantaneous (Fig. 220, A), at 

 other times it is preceded by a gradual decrease (Fig. 220, B). 

 The return to normal respiration is also preceded by an increase, 

 as in the turkey (Fig. 221). 



J-'io. 220. Apnoea from continuous ventilation in pigeons. (Luciani and Bordoni.) A, Instan- 

 taneous transition from normal breathing to apnoea, as soon as ventilation commences at V. 

 B shows transition from normal respiration to apnoea, after ventilation had commenced at 

 point V. 



(c) In fowls, apnoea is fairly difficult to obtain, no matter at 

 what pressure the pulmonary ventilation is effected. Generally 

 speaking, it is invariably incomplete, and respirations of an 

 extremely limited character can always be detected, showing 

 persistence of rhythmical activity in the centres (Fig. 222, A). 



FIG. 2-21. Gradual and delayed return of normal respiration after prolonged period of 

 apnoea in pigeons. (Lnciani and Bordoni.) 



Here also the return to the normal is preceded by an increase 

 (Fig. 222, B). 



(d) The apnoea of birds from continuous ventilation is, like that 

 of mammals (Berns), immediately interrupted by the insufflation 

 of a minute quantity of carbonic acid, as also by the momentary 

 closing of the ventral aperture, or of the inflating tube, or by 

 excitation of the vagi in the neck (Fig. 223). 



(e) When pulmonary ventilation is effected with pure oxygen 

 instead of air, at a pressure of 1 mm. Hg, complete apnoea is never 

 produced in pigeons (Fig. 224, A) ; at a pressure of 2 mm. Hg 



