RESPIBA TION. 457 



muscles, the other to contraction of expiratory muscles; hence they are spoken 

 of as inspiratory and expiratory parts of the respiratory centre, or as inspi- 

 ratory and expiratory centres. Moderate excitation of the inspiratory centre 

 causes not only contraction of inspiratory muscles, hut au increase in the 

 respiratory rate; and if the irritation be sufficiently strong, there occur- a 

 spasmodic arrest of the respiratory movements in the inspiratory phase. On 

 the contrary, excitation of the expiratory centre causes contraction of expi- 

 ratory muscles and diminishes the respiratory rate; powerful excitation of the 

 same centre is followed by arrest of movements in the expiratory phase. 

 The inspiratory portion may therefore be regarded not only as being spe- 

 cifically connected with inspiratory muscles, but in the sense of an accelerator 

 centre; and the expiratory portion maybe regarded as being similarly con- 

 nected with expiratory muscles, and as being an inhibitor)/ centre. When the 

 two are conjointly excited the accelerator effect prevails, because under ordinary 

 circumstances the accelerator element of the centre seems more excitable and 

 potent than the inhibitory ; therefore, when the centre as a whole is irritated, 

 it manifests an accelerator character. 



In addition to this centre, the existence of subsidiary centres is claimed, 

 situated both in the brain and in the spinal cord. One centre has been located 

 in the rabbit in the tuber cinereum, which has been named a polypnceic centre, 

 because when excited the respirations are rendered extremely frequent. The 

 sensitiveness of this centre is readily demonstrated by subjecting an animal 

 to a high external temperature, when a marked increase of the respiratory rate 

 follows; if now the tuber cinereum be destroyed, there occurs an immediate 

 cesssation of the accelerated movements. Another area has been located in 

 the optic thalamus in the floor of the third ventricle ; this centre is believed 

 to be excited by impulses carried by the nerves of sight and hearing, and 

 when irritated causes an acceleration of the respiratory rate, and when strongly 

 excited arrests respiration during the inspiratory phase ; hence it is regarded 

 as an inspiratory or accelerator centre. Another centre has been Located in 

 the anterior pair of the corpora quadrigeniina : it causes expiratory and inhibi- 

 tory effects, and may therefore be placed among the expiratory or inhibitory 

 centres. An inspiratory or accelerator centre has been recorded as existing in 

 the posterior pair of the corpora quadrigemina and the pons Varolii. The 

 nuclei of the triyemini are also said to act as inspiratory or accelerator centres. 

 Respiratory centres are likewise claimed to exist in the brain-cortex, h is 

 very doubtful, however, whether or not these so-called subsidiary respiratory 

 centres should be regarded as being of a specific character. In any event, we 

 cannot suppose that these centres are capable of evoking directly respiratory 

 movements, [f they exist, they are probably connected with the medullary 

 centre, through which (hey exert their influence on the respiratory movements. 

 The existence of a respiratory centre in the spinal cord is also doubtful. 

 The chief reason for the claim of its existence i< that respiratory movements 

 may for a time be observed after section of the cerebro-spinal ;i\i- at the junc- 

 tion of the spinal cord and bulb. In new-born animal- after such section 

 respiratory movements may continue for some time, strychnine rendering them 



