78 PHYSIOLOGY. 



ing. Grind up thoroughly in a mortar with about three parts of water. 

 After this has stood for ten or fifteen minutes, filter. Fill a test tube one- 

 third full of water, add a piece of starch half the size of a pea or less, and 

 boil the mixture to make starch-paste. Add the barley extract. Put in a 

 warm place and test from time to time with iodine. The first samples so 

 treated will be blue, later ones violet, brown, and finally colorless, showing 

 that the starch has all disappeared. This is due to the action of the dias- 

 tase which was present in the germinating seeds, and which was dissolved 

 out and added to the starch mixture. The office of this diastase is to 

 change the starch in the seeds to sugar. Germinating wheat is sweet, and 

 it is a matter of common observation that bread made from sprouted wheat 

 is sweet. 



(d) Put a little starch-paste in a test tube and cover it with saliva from 

 the mouth. After ten or fifteen minutes test with Fehling's solution. A 

 strong reaction appears showing how quickly and effectively saliva acts in 

 converting starch to sugar. Successive tests with iodine will show the 

 gradual disappearance of the starch. 



161. These experiments have shown us that diastase from three different 

 sources can act upon starch converting it into sugar. The active principle 

 in the saliva is an animal diastase (ptyalin), which is necessary as one step 

 in the digestion of starch food in animals. The taka diastase is derived 

 from a fungus (Eurotium oryzae) which feeds on the starch in rice grains 

 converting it into sugar which the fungus absorbs for food. The malt dias- 

 tase and leaf diastase are formed by the seed plants. That in seeds con- 

 verts the starch to sugar which is absorbed by the embryo for food. That 

 in the leaf converts the starch into sugar so that it can be transported to 

 other parts of the plant to be used in building new tissue, or to be stored 

 again in the form of starch (example, the potato, in seeds, etc.). The 

 starch is formed in the leaf during the daylight. The light renders the 

 leaf diastase inactive. But at night the leaf diastase becomes active and 

 converts the starch made during the day. Starch is not soluble in water, 

 while the sugar is, and the sugar in solution is thus easily transported 

 throughout the plant. In those green plants which do not form starch in 

 their leaves (sugar beet, corn, and many monocotyledons), grape sugar 

 and fruit sugar are formed in the green parts as the result of photosynthesis. 

 In some, like the corn, the grape sugar formed in the leaves is transported 

 to other parts of the plant, and some of it is stored up in the seed as starch. 

 In others like the sugar beet the glucose and fruit sugar formed in the 

 leaves flow to other parts of the plant, and much of it is stored up as cane 

 sugar in the beet root. The process of photosynthesis probably proceeds 

 in the same way in all cases up to the formation of the grape sugar and 

 fruit sugar in the leaves. In the beet, corn, etc., the process stops here, 

 while in the bean, clover, and most dicotyledons the process is carried one 

 step farther in the leaf and starch is formed. 



