REGULATION OF BREATHING 5 



oxygen and regulates the air-supply, thus playing the 

 part of a stoker who regulates the supply of both 

 fuel and air to a furnace. On the mechanistic theory 

 the regulation is automatic, and due to the working of 

 a mechanism connected with the fire. The latter 

 theory is of course the orthodox one at present. It 

 is not, however, these theories which I wish to discuss 

 in these lectures, but the character of the facts which 

 each of the two theories is an attempt to explain. 

 When the true character of these facts is realised it 

 seems to me that the old and ever recurring contro- 

 versy between mechanists and vitalists disappears. 



It has been known for more than a century that 

 breathing is dependent on the integrity of a very small 

 area of the brain in the medulla oblongata. When this 

 area, known as the respiratory centre, is destroyed 

 all signs of co-ordinated breathing efforts disappear. 

 Severance of the nervous connections between this 

 centre and the various respiratory muscles paralyses 

 these muscles ; but so long as any connections are left 

 respiratory efforts continue, and do so after severance 

 of the connections between the centre and the higher 

 parts of the brain. The action of this centre came to 

 be regarded as automatic, inspiratory and expiratory 

 impulses being alternately discharged from the centre 

 down the motor or efferent nerves leading to the 

 inspiratory or expiratory muscles, but no afferent 

 impulses being required to liberate these rhythmic dis- 

 charges. It was also found about the same time that 

 any interference with the supply of properly aerated 

 blood to the centre causes greatly increased activity 



