LABORATORY MANUAL OF PHYSIOLOGY. 



pare them with the changes of intrapulmonary pressure. In quiet 

 breathing, what is the constant condition of pressure in the thorax ? 

 How does this pressure change with inspiration and expiration? 

 Explain. 



Now close the tracheal cannula and induce asphyxia. Note the 

 variations in intrathoracic pressure during the violent respiratory 

 efforts which occur in this condition. 



For the influence of the respiratory movements on the blood 

 pressure and heart-beat, refer back to your blood-pressure tracings, 

 and study again the respiratory waves of the tracings. When is 

 the intrathoracic pressure lowest? when highest? What effect 

 would changes of pressure within the thorax have upon the pressure 

 of blood in the large arteries and veins and in the heart itself dur- 

 ing diastole ? 



IV. THE VAGUS NERVE IN RESPIRATION. 



The same rabbit that was used in the previous experiments may 

 be used for this. Continue the dissection of the neck region very 

 carefully, isolating both vagus nerves, and both superior laryn- 



FIG. 37. To Record Movements of Diaphragm. JR, Recording tambour ; B, rubber 

 bulb, connected with recording tambour ; D, diaphragm ; L, liver. 



geals. Make an incision through the abdominal wall below the 

 xyphoid appendix of the sternum, just large enough for the intro- 

 duction of a catheter over the end of which a collapsed rubber bal- 

 loon is tied. Pass this up between the diaphragm and the liver, on 



