18 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



milk prepared in (a). What color is the mixture? Keep in the water bath at 

 37 C., and observe from time to time. Does the color change? What does this 

 indicate? The action is of course upon the cream (fat) of the milk (Holmes, 

 p. 151). (R, L, A.) A similar lipase is secreted by the pancreas of the frog. 



3. Action of a diastase ptyalin. 



a) Test for starch: Place a few cubic centimeters of a i per cent starch paste 

 in a test tube and add a drop or two of iodine solution. A deep blue color results, 

 which proves the presence of starch. The nature of this blue compound which 

 iodine forms with starch is unknown. 



b) Test for sugar: Place a few cubic centimeters of glucose (fruit sugar) solu- 

 tion in a test tube, add a few drops of Fehling's solution, and heat to boiling. A 

 yellow, greenish, or red precipitate proves the presence of sugar. 



c) Test the starch paste with Fehling's solution. Is any sugar present in it? 



d) Test some saliva, spit out from your mouth, with Fehling's solution. Does 

 it contain any sugar? 



e) Action of saliva: Put about 5 c.c. of the starch paste in a test tube, and 

 spit some saliva from the mouth into it. Shake up thoroughly and place in the 

 water bath at 37 C. for several minutes. Remove and test with Fehling's solu- 

 tion. Is sugar present? Where did it come from? The enzyme in the saliva 

 which has this action is called ptyalin (from a Greek word meaning "spit"). An 

 enzyme having a similar action is secreted by the pancreas of the frog (the mouth 

 secretions of the frog have no digestive action). 



Explain fully in your notebook the action of these enzymes. State your 

 observations and interpret them. Consult Holmes, pp. 136-37, 142, 151. A 

 general textbook of physiology, obtainable in the library, will also be helpful. 



4. Absorption. This is the process by means of which the products of diges- 

 tion are transferred through the wall of the intestine into the blood and lymph 

 vessels for transport to all parts of the body. The process is impractical of 

 demonstration in the frog. 



D. FUNCTION OF THE RESPIRATORY SYSTEM; RESPIRATION, OXIDATION 



When any organic material burns, it uses up oxygen from the air and gives off 

 carbon dioxide. In exactly the same way living substance burns either itself 

 or the materials which it obtains from digestion, using up oxygen and releasing 

 carbon dioxide. All of the processes involved in this burning are called collec- 

 tively respiration. 



i. External respiration in the frog. The process and mechanisms involved 

 in getting the oxygen of the air into the body and throwing out the carbon dioxide 

 constitute external respiration. Obtain a live frog, place it in a covered dish 

 with a small amount of water, and after it has become quiet study the respiratory 

 movements. These consist of the opening and closure of the external nares, 



