RESPIRATION. 



breath. The fluid in the U will move synchronously with the 

 heart-beat. At each systole there will be an inspiratory move- 

 ment, and at each diastole an expiratory movement. 



II. PULMONARY PRESSURE. 



Place a rabbit under morphine narcosis. Anaesthetize lightly 

 with ether. Place, back down, on rabbit-board. Expose the 

 trachea through a median cervical incision. Introduce a tracheal 

 cannula. Connect this, through a T-tube, with the proximal end of 

 a mercury manometer. Place a clip on the rubber tubing, leading 

 from the T to the manometer, so that it can be either opened or 

 closed. At the beginning of an inspiration, open the manometer 

 clip and close the air-inlet limb of the T. At the height of inspira- 

 tion, close the clip on the manometer tube and open the air-inlet 

 tube. The inspiratory negative pressure may then be read off from 

 the manometer scale. A tracing of the respiratory movements 

 may be obtained in this way by partially occluding the air-inlet 

 tube. Close the air-inlet tube during several respiratory cycles. 

 Note the positive pressure of the expiratory phase and the negative 

 pressure of the inspiratory phase. After a few respiratory efforts 

 the animal will begin to struggle because of asphyxia. When this 

 occurs, note the change in the character of the respirations and the 

 great difference between inspiratory and expiratory pressure. In 

 quiet respiration, is the positive pressure in expiration much above 

 the atmospheric pressure ? 



III. INTRATHORACIC PRESSURE. 



Using the same rabbit as in the previous experiment, connect the 

 proximal limb of a manometer, through a piece of pressure tubing, 

 with a small glass tube. Make a small incision through the skin 

 over the fourth intercostal space on the right side. Make a very 

 small nick through the intercostal muscles and force the glass tube 

 through this opening. The tube should fit so tightly that there 

 will be no leakage of air around it. Note the movements of the 

 mercury in the manometer with inspiration and expiration. Com- 



