LESSON XXX 

 RESPIRATION (Continued) 



THE CIRCULATION IN THE LUNG OF THE FROG. PHENOMENA OF 

 INFLAMMATION. EFFECT OF CHANGES IN INTRATHORACIC 

 PRESSURE UPON THE LESSER CIRCUIT 



1. The Lung of the Frog. Pith a frog. Open its jaws widely, and 

 draw a small curved needle and silk thread through the soft tissues 

 around the orifice of the trachea. Insert the end of a straight glass 

 cannula in the tracheal orifice and secure it by means of the ligature. 

 Attach a short piece of rubber tubing to the cannula. . Open the ab- 

 dominal cavity of the frog widely. Blow air gently through the can- 

 nula until both lungs have been fully inflated. Kink the rubber tube 

 and apply a clip. Remove both lungs with the heart and suspend them 

 until thoroughly dried. 



Transilluminate them. Note the large central cavity in each as 

 well as the individual alveolar spaces along the wall. Cut each lung in 

 half and inspect its interior. 



2. The Capillary Circulation in the Frog's Lung. Pith a frog with- 

 out losing any blood. Block the opening by means of a pointed piece 

 of match. Proceed as has been described in paragraph 1, imparting to 

 the lungs a moderate degree of inflation. Raise one lung out of its cavity 

 and place it upon the glass fitted in the orifice of a plate of cork, such as 

 has been described upon page 99. 



Place a cover-slip upon the upper surface of this lung and apply 

 gentle pressure to flatten the latter. Study the blood flow under the 

 low and high powers of a microscope. 



Examine a preparation of injected pulmonary capillaries under the 

 microscope. 



3. Phenomena of Inflammation. Allow a drop of a dilute solution 

 of mustard to be drawn by capillarity under the glass covering the sur- 

 face of this lung. Study the resultant phenomena of inflammation as 

 exemplified by changes in the circulation, viz., the relaxation of the 

 capillaries, the retardation of the flow, the greater vascularity of this 

 part, the gradually increasing numbers of white blood-cells, the fixa- 

 tion of these cells to the walls of the vessels, and their final migration 

 into the neighboring tissues. 



4. Effect of Variations in Intrathoracic Pressure Upon the Blood- 

 flow Through the Lungs. With the help of the apparatus represented 

 in Fig. 92 study the effect of the inspiratory increase and expiratory 

 decrease in intrathoracic pressure upon the blood-flow. The large 

 orifice of a bell-jar is closed with a rubber membrane. To its central 



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