of water overnight. Test the material in both the bottles and the jars for the 

 appropriate substances.^ 



2 To find out whether digestion takes place during germination, test the coty- 

 ledons and endosperms (ci) of several dry seeds for starch and simple sugar and 

 (b) of similar seeds after they have sprouted. Compare and explain your findings. 



3 To extract the starch-splitting enzyme diastase from germinating seeds 

 and grains, grind a mass of seedlings in which the sprouts are about half an inch 

 long in a mortar; just cover with water and let mass stand a half hour. Filter off 

 clear liquid and test for diastase by trying to digest starch with it. 



4 To show the digestion of starch by saliva and by diastase, mix dilute starch 

 paste with saliva and with diastase, set it in a warm room overnight, and then 

 test for simple sugar and for starch. Do tests on saliva, diastase and starch paste, 

 as well as on the mixtures which have stood overnight. Account for your results. 



5 To demonstrate the effect of rennin on milk, add a little rennin, dissolved 

 in water, to a cup of fresh, lukewarm milk, and let stand for ten minutes." (Ren- 

 nin acts on milk in the stomachs of animals as it does on the milk in the vessel.) 

 What relation has this action to digestion? 



6 To find out how proteins are digested in the human body, expose small 

 cubes of boiled egg white to the different digestive fluids and note the effects.^ 

 Gather some saliva in a test tube. Place protein cubes in four test tubes contain- 

 ing respectively (a) water, (h) saliva, (c) gastric juice, and (d) pancreatic juice. 

 Leave all together in a warm part of the room or in a laboratory incubator. The 

 next day examine the cubes of protein to determine whether and how much they 

 have been "eaten away". Tabulate results observed and note conclusions. 



7 To study the digestive organs and their movements: 



To observe peristalsis, kill a suitable animal quickly, and open the abdomen 

 to expose the large intestine.* 



^For starch, test with iodine (see page 157). 



For simple sugars, as grape sugar or glucose, use Fehling solutions. Add about 5 cc of 

 Fehling copper solution to the solution to be tested, and boil for a few minutes. Then add 

 a similar amount of Fehling alkaline solution. If a slight amount of sugar is present, the 

 color will be green; if more is present, yellow; if still more, orange; and if there is a con- 

 siderable amount, red. 



For the liquid fats, observe the fluid in the botde and in the jar to see if any oily drops 

 are present. (To test for fats in solid substances, crush them, pour on ether to dissolve 

 any fat present, then pour ether on a piece of paper. A permanent translucent spot indicates 

 presence of fat.) 



For proteins, add a few cubic centimeters of nitric acid, and heat. Nitric acid turns pro- 

 teins to a yellow color. If sufficient sodium hydroxide is then added to make the soludon 

 alkaline, the protein turns an orange color. 



-Rennin is available in various trade preparations. 



^To make artificial gastric juice, dissolve dry pepsin in water and add a few drops of 

 hydrochloric acid. To make ardficial pancreatic juice, add pancreatin to water, with a small 

 pinch of sodium bicarbonate. 



''Frogs, chickens, rats and guinea-pigs are all suitable for use in this study. It is interest- 

 ing to use all of them, for the internal structures vary significandy. To observe peristalsis, 

 open the animal immediately after it is anesthetized. The frog may be "pithed" by quickly de- 

 stroying the brain with a needle or a sharp knife. 



183 



