xin RESPIRATORY RHYTHM 491 



having demonstrated that the respiratory acts are normally deter- 

 mined by the carbonic acid circulating in the centres. Baglioni 

 and Winterstein aptly pointed out that in Fredericq's experiment 

 the vagi were left intact. Now, when the excitability of the 

 respiratory centres is altered, it is quite conceivable that the 

 excitations of the pulmonary terminations of the vagi, which 

 normally exert a reflex control over the acts of respiration, may 

 determine an inhibition of the centres, and thus produce spurious 

 apnoea. That in Fredericq's cases the excitability of the centres 

 was enormously depressed may be inferrecNhrom the narcosis (due 

 to the morphin or chloroform administered), the operations 

 necessary to produce the crossed circulation in the brain, the 

 diminished blood-supply to the brain (ligature of vertebral 



FIG. 227. Pneumograms obtained from two Knoll's pnetimographs in two dogs (A and B) during 

 experimental crossed circulation. (Fredericq.) The blood from trunk of B circulates in head of 

 A; that from trunk A in head B. Each application of artificial respiration in B produces a 

 short period of apnoea in A. 



arteries), and lastly, the general intoxication of the centres due 

 to the injection of pro-peptone, which induces a quasi-comatose 

 state. It is also conceivable that under such conditions the sum 

 of the excitations which reach the bulbar centres continuously 

 by the afferent paths of the pulmonary vagi, the muscles, fascia, 

 tendons, determine a brief inhibition of the respiratory movements. 

 We say brief, because Fredericq has not demonstrated that pro- 

 longed artificial respiration in dog B determines any apnoeic state 

 of corresponding duration in dog A. 



The tracings of Fig. 22*7, on the other hand, demonstrate that 

 in two repeated experiments five strong pulmonary insufflations 

 on dog B determine a suspension of respiration in dog A lasting 

 8-10 seconds, after which natural respiration re-commences very 

 feebly, in accordance with the depressed excitability of the centres. 



