REGULATION OF RESPIRATORY MOVEMENTS 1221 



respiration is shown still more strikingly if the respiratory centre 

 in the medulla be separated from the higher parts of the brain before 

 the section of the vagi is carried out. Separation of the medulla 

 from the higher parts of the brain, as by section just behind the corpora 

 quadrigernina, has practically no influence on the respiratory rhythm. 

 If now both vagi be divided the normal respiratory movements cease 

 entirely, being replaced by a series of inspiratory spasms, each of which 

 lasts several seconds and is followed by a pause of half to one minute's 

 duration. These spasms are inadequate for the proper oxygenation 



of the blood. They become gradually less and less frequent, and in 

 about half an hour the animal dies of asphyxia. We must conclude 

 therefore that the medullary respiratory centre with the help of the 

 vagi is able to carry out normal respiratory movements. If both vagi 

 are cut, impulses arrive at the centre from the higher parts of the 

 brain regulating its activity, and enabling it to carry out modified 

 but sufficient respiratory movements. Removed from both these 

 sources of afferent impulses, the centre discharges only a series of spasms 

 which are totally inadequate for the renewal of the blood-gases, so that 

 the animal dies. 



We may summarise these results as follows : 



Respiratory centre with vagi- normal respiration. 



Respiratory centre with brain modified respiration. 



Respiratory centre alone inadequate spasmodic contractions of 

 respiratory muscles, and death of animal. 



The nature of the supplemental action of the mid-brain on the medullary 

 respiratory centre has not yet been made out. It is apparently not dependent 

 on afferent impulses arriving at the brain, since section of no cranial nerve 



