xin RESPIRATORY RHYTHM 463 



According to Patrizi aud Fraiichini, the diaphragmatic arrest 

 on stimulation of the central trunks of the vagus is not invariably 

 (in profoundly anaesthetised animals) the effect of predominance of 

 the excitatory muscles, but may be merely an inhibitory suspension. 

 Whatever the phase in which the diaphragm is overtaken by the 

 appropriately graduated stimulation of the vagus, it becomes 

 immobilised without change of tone (level of record), and completes 

 its movement at the close of the inhibitory respiratory effect, 

 resuming it from the point at which it had been interrupted. 

 They do not deny that excitation of the vagus may, at a certain 

 point, produce respiratory movements, since they more than once 

 had occasion to verify that particular result ; but they do affirm 

 that the respiratory arrest on centripetal stimulation of the vagus 

 is not seldom a merely inhibitory phenomenon. 



Treves (1905) also admits that the effects of faradisation of 

 the central end of the vagus are inhibitory in character. After 

 eliminating the action of the principal expiratory muscles by 

 ligature of the cord at a point below the origin of the phrenic 

 nerve, he found that section of the vagus was followed by more 

 intense respirations, and sometimes by a prolonged inspiratory 

 tetanus, interrupted only by passive expirations, which became 

 more and more frequent, and irregular in their rhythm and ampli- 

 tude. Under these conditions the excitation of the central end 

 of the vagus had a constant inhibitory effect, reducing the depth 

 of the inspiratory act, and the frequency of respiration may 

 be augmented or diminished according to the more or less pro- 

 nounced tetanic character of the respiration after section of the 

 vagus. 



VII. Besides the pulmonary fibres of the vagus, other influences 

 may affect the rhythmical impulses of the bulbar respiratory 

 centres. These may emanate from the cerebral centres, or from 

 the periphery of the centripetal nerves in general, and particularly 

 of the sensory nerves, with which the mucosa of the nasal, 

 buccal, pharyngeal, laryngeal and tracheal air-passages are 

 provided. 



The afferent influences from the cerebral centres to the bulbar 

 centres of respiration are conspicuous after section of the vagi. 

 The respiratory type, which, as we have seen (Fig. 211), follows 

 immediately on this operation, depends on and is specially 

 maintained by the active intervention of the cerebral centres, in 

 lieu of the missing regulatory influence of the vagi. To prove 

 this, it is only necessary to compare the effects of separation of 

 brain from bulb in animals with intact and with divided vagi. 

 In the former, as we know, the normal respiratory type is not 

 greatly modified after a transitory disturbance due to the traumatic 

 effects of the operation; in the latter, on the contrary, extraordinary 

 changes in the mode of respiration ensue. The respiratory move- 



