GENERAL PHYSIOLOGY OF THE FROG 19 



rise and fall of the floor of the buccal cavity, and contraction and expansion of 

 the sides of the body. Time the rate of each of the movements. Can you discover 

 any correlation between any of these movements? Does the frog respire in the 

 same manner as the human (R, L, A)? Read Holmes, pp. 168-177, understand 

 thoroughly the mechanism of respiration in the frog and write an account of it 

 in your notebook. 



2. Respiratory activity of the skin. Demonstration experiment. Three 

 jars, each containing a frog, are placed in a trough of running water, so that the 

 temperature of all is the same. One is filled with running water, the second with 

 standing water, so that all bubbles of air are entirely excluded, and the third has 

 an inch or two of water in the bottom. Do the frogs immersed in water show 

 respiratory movements? How do they get oxygen? What is the condition of 

 the three frogs after two or three days? Explain fully in your notebook. 



3. Carbon dioxide output. The following simple experiment demonstrates 

 that carbon dioxide is given off from the lungs. (This need not be performed by 

 those familiar with it.) A bottle is furnished containing two or three inches of 

 lime water or saturated solution of barium hydroxide, and provided with two 

 tubes, one of which extends below the lime water while the other does not. First 

 draw atmospheric air through the lime water by sucking on the shorter tube. 

 Does atmospheric air contain enough carbon dioxide to produce a precipitate 

 with lime water? Then blow air from the lungs into the longer tube. What 

 happens? Explain fully (A). 



4. Internal respiration or oxidation. The respiratory movements considered 

 in sections i and 2 are merely methods for getting the oxygen into the body and 

 into the blood. The actual use of the oxygen by the living substance of the 

 animal is the real process of respiration. To avoid confusion, this process is 

 designated as internal respiration, or oxidation. 



E. FUNCTION OF THE EXCRETORY SYSTEM; EXCRETION 



Every part of the organism as the result of its activities gives off waste 

 matters. Those derived from the oxidation of fats and carbohydrates are mainly 

 carbon dioxide and water, which are cast off through the lungs and skin. Those 

 derived from the oxidation of proteins, or other chemical splittings of proteins, 

 contain nitrogen, and these nitrogenous wastes are taken from the blood and 

 lymph by the kidneys and eliminated from the body. This function of the 

 kidneys is called excretion. The student should note that excretion is an active 

 process, which is concerned with the elimination of soluble materials which have 

 once been a part of the body; therefore the purely passive ejection of undigestible 

 materials from the intestine is NOT excretion, and should not be confused with that 

 process, as students are prone to do. Such undigested food in the intestine is 

 designated as feces, and its passage from the body is the process of defecation 

 or egestion. 



