RESPIRATION 135 



space is a capillary space filled with pleural fluid. This implies that the 

 surface of the lung is everywhere in close contact with the inner surface 

 of the wall of the thorax. 



(6) Forced Respiration. Lower and raise the "diaphragm" more 

 forcibly, thereby producing a more ample expansion of the "lung" and 

 more decisive variations in pressure. 



(c) Dyspnea and Asphyxia. The former condition may be repro- 

 duced in a mechanical way by partially closing the stop-cock with which 

 the inlet tube is equipped. This would correspond to an incomplete 

 closure of the trachea and would greatly impair the interchange of the 

 respiratory air. Note the resistance now acting against the "dia- 

 phragm." Obviously, this diminution in the caliber of the inlet tube 

 must augment the variations in the intrapleural and intrapulmonic 

 pressures. 



Close the stop-cock completely, simulating the condition of asphyxia, 

 or complete absence of air. 



(d) Collapse of the Lungs. Expand the "lung" by moving the 

 "diaphragm" downward. Suddenly permit air to rush into the "intra- 

 pleural" space by slightly tilting the rubber cork closing the upper 

 orifice of the bell-jar. Observe the immediate loss of "intrapleural" 

 pressure and collapse of the "lung." Having in this way destroyed the 

 "intrapleural" pressure, endeavor to expand the "lung" by moving the 

 "diaphragm" downward. 



3. Application of Above Principles to the Thorax of the Mammal. 

 Anesthetize a cat and maintain the anesthesia throughout the following 

 experiments: Perform tracheotomy. Make a median incision through 

 the skin in the midventral line of the body, beginning near the tip of 

 the sternum and extending well along the linea alba. Reflect the 

 skin on each side so as to expose the ventral aspect of the thorax. Study 

 the mechanism of normal respiration. Note the excursions of the 

 diaphragm and contraction of the neighboring intercostal muscles. 

 Observe the downward movement of the liver and stomach on inspira- 

 tion. Which part of the chest is affected most in quiet breathing? 

 Produce forced respiration by partially closing the rubber tube attached 

 to the tracheal cannula. The normally diaphragmatic type of respira- 

 tion is now gradually augmented by costal respiration. Observe also 

 that the accessory movements of respiration are now much more con- 

 spicuous. 



4. Action of the Diaphragm. Open the abdominal cavity by an 

 incision through the linea alba. Retract the margins of the wound and 

 depress the liver. Observe: (a) The muscular and tendinous portions 

 of the diaphragm, (6) the general shape of this septum, (c) the course 

 of the fibers composing its muscular part, (d) the manner of attachment 

 and insertion of these fibers, and (e) the character of their contraction. 



Determine the distance traversed by the tendinous portion of the 

 diaphragm on quiet inspiration. Identify the complemental space, 

 bounded by the upper surface of the diaphragm and the opposite wall 



