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 
