ABOUT STARCH. 



197 



It is in the structural centre of the grain. If the drying is cur- 

 ried far enough, cracks may be seen extending from the nucleus. 

 They generally radiate, looking something like a star. Sometimes 

 one long crack runs the greater part of the length of the grain. 

 The cracks may and may not reach the surface. Taking all these 

 facts together we can draw the fair conclusion ; that the layers 

 differ in density; that the inner layers are softer than the outer, 

 because they contain successively more water ; that the water is 

 driven off by the heat and the consequent vacuity appears, form- 

 ing the " nucleus," where there is most water, that is, in the inner- 

 most layers ; that farther drying causes cracks to appear in the 

 harder layers, the longer the drying the more extensive the cracks. 



Further evidence in favor of this explanation of the starch- 

 grain is afforded by the action of hot water and chemicals. If a 

 little starch is boiled, the grains swell, burst and emit much glairy 

 matter. At the same time a thin pellicle sinks to the bottom and 

 is only gradually absorbed. These phenomena can be partially 

 seen in a test-tube. They can be watched under the microscope 

 if the observer has the apparatus for heating his slide without in- 

 juring his objectives. For those who are without this apparatus, 

 perhaps the best way is to deposit a little starch with two or three 

 drops of water on a glass slide, and then boil the water down 

 without the application of too much heat. The slide should be 

 allowed to cool before it is placed under the microscope. Starch 

 can then be seen arrested in every stage of solution. One is 

 apparently untouched ; another is slightly swelled ; another is 

 much swelled at one end ; still another is just ready to burst. 



A similar series of phenomena can be seen by the application of 

 caustic potash. Arrange a slide as before, for the application of 

 iodine and treat in the same manner. The approach of the re- 

 agent causes a great commotion among the starch grains. They 

 become uneasy, dance about, and finally sweep away. to the other 

 side of their limits. To see the action of the potash well, one 

 must select a field easily accessible to the reagent, but where the 

 exit of the grains is prevented by an air-bubble or bit of tissue 

 just behind them. That being the case, the grains advise the ob- 

 server of the approach of the potash by becoming very uneasy. 

 As it strikes them they begin to swell, the swelling extending 

 down their length as the potash advances. The swelling is mostly 

 lateral, and what was an ovoid body before becomes a broad disk. 



