5 To observe the effect of exercise on the rate of breathing, record the rate 

 of breathing before and after exercise. Use a graph to show the individual varia- 

 tions, as well as the relation between the amount of exercise and the rate of 

 breathing. 



6 To demonstrate the effect of exercise on the excretion of carbon dioxide, 

 compare the length of time it takes to turn a measured amount of pink phenol- 

 phthalein colorless, by exhaling through it with a glass tube before exercising, and 

 through a similar amount immediately after exercising. 



7 Examine the sides of the abdomen and the under surface of the thorax of 

 a large grasshopper (or other insect) for spiracles, or breathing pores. Observe in 

 a live insect at rest the body movements which would tend to move air through 

 these holes. Dissect the animal under water and identify the air-tubes, or tracheae, 

 which carry air to all parts of the body. Examine some of these tubes under the 

 microscope. 



8 To study the structure of gills, dissect the mouth and the gill cover of a 

 fish, exposing the gills. Note their position with reference to water which flows 

 through the mouth and out under the gill covers. Examine a small portion of the 

 gill with the microscope and note its feathery texture. 



9 To study the respiration of a frog, place a frog in an aquarium or large 

 jar of water so that it cannot rise to the surface except by swimming. Note 

 whether the frog comes to the surface to breathe. How can it carry on respiration 

 when beneath the surface.'* Is there anything to show that the animal is suffering 

 for lack of air if it is kept from coming to the surface for several minutes.'* Re- 

 move the frog from the aquarium and place it on a table. Watch movements of 

 the throat and of the abdomen, and describe their relations to getting air into and 

 out of the animal's lungs. Contrast the breathing of a frog with that of a mammal. 



QUESTIONS 



1 What is the source from which living cells ultimately get oxygen, and what 

 eventually becomes of the waste gases which living cells liberate.'* 



2 Since living matter oxidizes itself, how do animals nevertheless keep on 

 living.'* 



3 What different special oxygen-carrying substances are found in different 

 species .'* 



4 In many-celled organisms, how do cells remote from the surface get their 

 oxygen supply? 



5 What conditions within the body influence the rate of respiration.? 



6 How do organisms without breathing organs respire.? 



7 How does the breathing of the frog resemble that of the fish ? How do the 

 two differ.? 



8 How does the breathing of a frog resemble that of a bird.? How do the 

 two differ? 



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