RESPIRATION 107 



3. To Study the Intrathoracic Pressure. Locate an intercostal 

 space to the right of the sternum and opposite its middle point. 

 Make an incision 1 cm. long, parallel with the intercostal space and 



1 cm. from the sternum. Dissect through the intercostal muscles, 

 taking care not to cut the pleura. Insert into the wound the point 

 of the glass cannula, previously provided with a rubber tube which 

 is clamped, and press it carefully through the pleura into the right 

 pleural cavity. 



Join the rubber tube to a recording tambour and unclamp. Slowly 

 and gently manipulate the cannula until there is evident communica- 

 tion through the lumen of the cannula and tube from the pleural 

 cavity to the tambour. 



So adjust the cannula that the recording lever makes the maximum 

 excursion. Bring the levers into such a relation to the kymograph 

 that the tracing point of the stethograph lever shall be vertically 

 over that of the lever which is to record intrathoracic pressure, and 



2 cm. to 3 cm. from it. 



Trace upon the drum a stethogram and chronogram as well as 

 an intrathoracic pressure record, taking care that the tracing points 

 of the recording tambours are in a vertical line. 



(1) Does the rhythm of varying pressure correspond to the rhythm 

 of the respiratory movements? 



(2) If so, does that necessarily establish between them the relation 

 of cause and effect? 



(3) What change of pressure is indicated by the rise of the pressure 

 lever? 



(4) What movement of the pressure lever corresponds to a rise 

 of the stethograph lever? 



(5) What is the condition of intrathoracic pressure during inspira- 

 tion? During expiration? 



(6) Stop the entrance of the air into the respiratory passages by 

 closing the rabbit's nostrils. What effect does this have upon the 

 respiratory movements? 



(7) Is the intrathoracic pressure affected by the experiment? If 

 so, explain the effect. 



(8) If two phenomena correspond perfectly in their cycles, and if 

 a variation of one is always accompanied by a variation in the other, 

 can there be any reasonable doubt that they sustain to each other 

 the relation of cause and effect? 



(9) Is one of the phenomena in question the cause of the other? 

 If so, state which is the cause and establish your position. 



(10) Clamp the rubber tube of the pressure apparatus. Replace 

 the recording tambour with a water manometer. Unclamp. Is the 

 pressure during inspiration positive or negative, and how much? 



(11) Is the pressure during expiration positive or negative, and 

 how much? 



