RESPIRATION 



477 



FIG. 263 



diaphragm slightly descends, for the falling-in of air is impossible. Note 

 the great changes of pressure as shown in the manometer in connection 

 with the pleural cavity. 



C. Pneumothorax. Pull out the glass plug which closes the tube 

 connected with the pleural cavity. The diaphragm now descends with 

 great freedom, but no air falls into the lung because no distending suction 

 outward is exerted on the lung- walls. The 

 weight of the atmosphere is equalled by that 

 of the air outside the lung in the pleural 

 cavity. 



Expt. 31. Respiration in the Frog. (Ob- 

 servation only. ) The frog has no diaphragm, 

 but makes the muscles of the floor of his 

 large mouth-cavity serve the same purpose, 

 with the important difference that whereas 

 the descent of the diaphragm in birds and 

 mammals sucks the air into the lungs, here 

 the mouth-floor muscles push it in with a 

 true bellows-like movement. 



Observe the rhythmic movements of these 

 muscles; the rhythm is easily disturbed by 

 handling, etc., but not stopped long while 

 the animal is in the air. While submerged 

 in the water the frog gets oxygen only 

 through its skin. Note the closure of the 

 nostrils at each inspiration. They are 

 the automatic valves of these inspiratory 

 bellows, opening to admit the air and closing 

 promptly to prevent its return, thus forcing 

 it to enter the lungs, the glottis opening as 

 the nostrils close. 



Expiration is here more of an active pro- 

 cess than in mammals; the muscles along 

 the sides of the body-cavity compress the 

 viscera and so the lungs, the air passing out 

 in a quick spurt through the opened nares. 



Expt. 32. The Breath-rate of Anolis. 

 The Normal Stethogram. (See Chapter 

 on Respiration.) (Apparatus : Anolis stetho- 

 graph, and kymograph.) Adjust the stetho- 

 graph for writing on the smoked drum 

 by means of the aluminum heart-lever. Fasten the lizard (Florida 

 "chameleon") on the board so as to be immovable but uninjured in 

 any way, strapping down firmly the tail and, if necessary, the head. 

 Adjust the animal within the stethograph so that the latter's levers press 

 evenly on either side of the body where the respiratory movement is 

 greatest, close to the forelegs. Warm the animal up somewhat if 



Lungs' of the chameleon (Cha- 

 meleo vulgans). (Wiedersheim.) 

 Observe their relatively great size 

 and their simple sacculation. 



