xiii RESPIRATORY RHYTHM 457 



depend the contractions of the different groups of muscles that 

 serve in respiration, are not true respiratory centres, since lihey 

 are not perfectly autonomous, and require a co-ordinating centre in 

 the bulb, which is the sole organ on which respiratory stimuli act, 

 and is alone capable of elaborating them so as to throw the spinal 

 centres into activity. He opposes the theory of decentralisation 

 by one of centralisation. The difference between the two theories 

 seems, however, to lie in the name rather than in the conception. 

 In. our opinion the real problem (which has so far remained 

 unanswered) is the more exact definition of the nature of the 

 co-ordinating function of the bulbar respiratory centre. Do the 

 various modes of functional association and succession of the 

 several muscles or groups of respiratory muscles depend exclusively 

 on this ; or do the respective spinal centres also co-operate actively ; 

 or (at the least) is the varying degree of excitability of these centres 

 at the given moment in which they receive the impulses from the 

 bulbar centre, of account ? 



Nothing definite, again, is known as to the localisation of the 

 supposed subordinate inspiratory and expiratory centres. We 

 only know that in both categories we must distinguish between 

 the centres of the cerebral, bulbar, and spinal segments, which 

 enormously complicates the problem of their localisation. 



VI. In view of the well-established fact that under normal 

 vital conditions, with the senses and all the mental emotions at 

 rest, the respiratory movements are completed involuntarily, in 

 consequence of rhythmically alternating impulses, from the 

 inspiratory and expiratory bulbar centres, the question arises 

 whether these impulses are automatic or reflex in character, i.e., 

 whether they are the effects of rhythmical changes intrinsic to the 

 centres, or depend upon rhythmic or continuous stimuli, coming 

 to them from without ? In order to determine this point, which 

 is of fundamental importance, we must first of all examine how 

 they are affected by the various afferent nerves, with which they 

 are in direct anatomical and physiological relation. Among these 

 in the first place is the Vagus. 



The cervical trunk of every vagus nerve contains afferent 

 fibres coming from the lung, and passing to the bulbar respiratory 

 centre. From the terminal ramifications of these fibres in the 

 lungs, rhythmical excitations pass to the centres, and are capable 

 of throwing them into activity, or considerably modifying their 

 intrinsic energy. This is clear from the experimental researches 

 of Rufus of Ephesus, Galen, and Legallois (1812). 



When the trunk of one vagus is suddenly divided in the neck, 

 while the animal breathes air regularly from a large closed cylinder, 

 connected with a Marey's writing tambour, which registers the 

 oscillations of tracheal pressure, the respiratory type changes ipso 

 facto ; the breathing becomes more excursive and less frequent, 



