Structure of the starch-grain. 



Proceedings of the Section of Sciences, Kon. Akademie van Wetenschappen, Amster- 

 dam, Vol. XIV, 1912, p. 11071110. Verscheen onder den titel De bouw der zet- 

 meelkorrel in Verslagen Kon. Akademie van Wetenschappen, Wis-en Natuurk. Afd., 



Deel XX, 1912, biz. 1252 1256. 



If one gram of potato-starch is boiled with 100 cM 3 of distilled water this is just 

 sufficient to bring the grains to their maximum of swelling and make the starch 

 take up about 70% of the water so that it remains suspended and cannot precipitate, 

 as the swollen grains touch one another. Each grain swells thereby to a somewhat 

 irregular globule whose diameter is about 3. 5 times that before the ebullition. Whether 

 the boiling lasts shorter or longer is of no consequence. If more water is used for the 

 boiling no further swelling takes place; when left to sedimentation the liquid above 

 the starch colours but feebly blue with iodine. 



When a microscopic preparation is made, containing but few starch-grains, and 

 a strong tannin solution flows sideways under the cover-glass, the following is seen 

 (compare the figure). 



At the moment the tannin comes into contact with them, the grains, which at 

 first sight seem homogeneous, show a very distinct membrane through which the tannin 

 easily diffuses to the inside where it directly forms a characteristic precipitate. When 

 using a more dilute solution 1 ) this precipitate consists of little droplets in very lively 

 Brownian movement and with a more concentrated tannin solution, of solid particles, 

 adhering together and filling up the whole inner space of the vesicle. This experiment 

 is so simple and convincing that it cannot be doubted for a moment but the boiled 

 starch-grain consists of a solid, sac-shaped, quite closed wall, containing a liquid. 



How it is possible that this fact seems unknown I cannot understand, but I have 

 nowhere found it mentioned in the extensive literature about this subject. 



The liquid in the vesicle is a granulose solution, or as is said at the present day, 

 an amylose solution, containing 0.6 gram of the i gr. originally used, which diffuses 

 but with difficultly through the walls into the surrounding water. If, however, the 

 boiled starch is rubbed fine with sand the delicate sacs burst and the granulose 

 solution diffuses in the water, which then becomes intensely blue with iodine. 



That the wall consists of a very soft substance may be observed as well by its 

 great variability of shape at pressure, as by the ease with which it is distended to 

 short threads by moving the cover-glass, to which it adheres, when touched by it. 



*) Very much diluted tannin solutions give no precipitate at all with starch or 

 granulose solutions. 



