PROBLEM 208 241 



Troblem 207: To compare the structures of the lungs of the 

 frog and of man. 



Materials. — Freshly killed frogs, blowpipes, charts or models 

 of human lungs. 



Method. — Open a frog's mouth and find the sUtlike opening 

 {glottis) just back of the tongue. Insert a blowpipe or a glass 

 tube and blow down the short windpipe (trachea) which branches 

 into two divisions leading to the lungs (bronchial tubes). 



Observations. — What happens to the lungs ? Examine a 

 section cut through a frog's lung. Is it hollow? Now compare 

 the baglike lungs of the frog with the more complicated lungs of 

 man (see chart). Do you find the same structures leading to 

 the lungs of man? 



Note. — The windpipe divides as in tiie frog, one tube going to each lung. The 

 tubes now divide like the branches of a tree in smaller tubes (the bronchial tubes) 

 which end in grapelike masses of small thin- walled sacs called alveoli. 



Which part of the lungs of man would be elastic? Of the 

 frog ? Why ? 



If blood vessels were found in the walls of these sacs, what gas 

 might be brought in the blood to this point ? What gas might be 

 in the air? How might the exchange of these gases take place? 

 Where might it take place? 



Conclusion. — 1. How do the frog's lungs differ from those of 

 a man? 



2. Explain how the structure of the lungs gives a large area of 

 moist membrane' separating the blood on the one hand from the 

 air on the other. 



3. What is in the blood that might get to the air? 



4. What is in the air that might get into the blood ? 



Problem 208 : To determine changes that take place in air 

 in the lungs. 



Note. — changes have already been noted that take place in blood within the 

 lungs. Our next problem is to see what changes take place in air within the lungs. 



Materials. — Thermometer, glass plate, hmewater, glass tubing, 

 test tube, glass jar, diagram, page 334, Civic Biology. 



Observations. — Breathe on the bulb of a thermometer and re- 



HUNTEB LAB. PBOB. 16 



