78 PHYSIOLOGY. 



ing. Grind up thoroughly in a mortar with about thri-c parts of water. 

 After this has stood for ten cir fifteen minutes, filter. ]''ill a test tube one- 

 third full iif water, add a piece of starrh half the size of a pea or le.ss, and 

 boil the nii.\ture to make starch-paste. ,-\dd the barley extract. Put in a 

 warm ]ilace and lest from time to time with iodine. The first samples so 

 treated will be blue, later ones violet, brown, and fmally colorless, .sh(nving 

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

 tase \\hich was present in the germinating seeds, and wlu( h. was dissoKx-d 

 oiU and added to the starch mi.\ture. The ^iflice 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 si)routed wheat 

 is sweet. 



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

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

 .strong reaction appears showing how (piickh" and effectivelv sali\'a acts in 

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

 graflual disa[)]:)earance of the starch. 



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

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

 in the saliva is an animal diastase (ptyalvi), which is neci-.s.sary as <jne aU-]i 

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

 from a fungus (Kurotium oryza;) 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 eiubr\-o fo?- foinl. That 

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

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

 again in the form of starch (cxam]ile, (he 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 liecomes active and 

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

 while the sugar is, and the sugar in soluliiai is thus easily IransporU'il 

 throughout the plant. In those green ]>lants wliicli do Udl foi in starch in 

 their lea^'es (sugar beet, corn, and man\- momn (it^'K'dims), grape sugar 

 and fruit sugar are formed in the green ]>arts as the resiiU of j'h.otosN-nthesis. 

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

 to other parts of the plant, and some of it is stor(.'(] uji in the scL'd as slarch. 

 In others like the sugar beet the glucose and fruit sugar fiirnu-d in (he 

 (eaves flow to other parts of the plant, and much of it is slorcd up as cane 

 sugar in the beet root. The jirocess of pholos\'n[liesis probabb' proceeds 

 in the same way in all cases up to (he foriua'.ion of (he grape sugar and 

 fruit sugar in the leaves. In the beet, corn, etc., the process s(ops here, 

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

 step farther in the leaf and starch is formitd. 



