ADVANCED EXPERIMENTAL PHYSIOLOGY 



165 



Excitation produces either a slight rise (pressor effect) or a slight 

 fall (depressor effect) of pressure. The heart rate is reflexedly 

 slowed, and the respiration is stopped with the diaphragm in 

 inspiratory spasm. 



The electrodes are next transferred to the central end of the 

 depressor nerve. On excitation the blood-pressure slowly falls, 

 and remains at a lower level so long as the excitation is maintained. 

 The rhythm of the heart is as a rule unaffected. The second vagus 



FIG. 155. Bering's apparatus for demonstrating the action of the respiratory 



pump. 



A, Glass bell, thorax ; B, air-tight base ; K, diaphragm ; C, trachea leading to lungs ; I, mano- 

 meter ; E, tube opening into A ; F, heart with valves V. The action of the diaphragm 

 pumps air in and out of the lungs and water through the heart. The lungs and heart are thin 

 rubber bags. 



nerve is now exposed and divided. The heart beats more rapidly, 

 and the arterial pressure rises. The vagus centre tonically controls 

 the rhythm of the heart. 



Asphyxia. The trachea is clamped. Note the sequence of 

 events. 



1st stage : Respirations deeper and more ample ; the beating 

 of the heart is accelerated and more forcible. 



