Starched microscope slide

The coacervate drops coming in contact with the glass surface of the slide soon become invisible as a result of wetting. To prevent this starched microscope slides may be used (see p. 435). 

Coacervates of all kinds of types, provided the colloid belongs to the hydrophilic type, wet a glass surface and spread over it when they settle on it from the equilibrium liquid. We have already mentioned (p. 339, note 3) that covering the glass surface with a dried layer of amylum solubile prevents this spread as a result of which such starched microscope slides form an indispensible aid in the microscopic study of the colloid morphology of these coacervates. 

Carbon and carmine particles are also taken up (Fig. 2 b) but amylum grains merely attach themselves to the outside of the coacervate drops. This is in agreement with the difficult wettability of a starched microscope slide by coacervate drops. 

With suitable coacervate objects one may observe that currents " occur in coacerv-ate drops restit on a starched microscope slide (p. 435) when a sufficiently stroi dif-fusionfield is produced, in the equilibrium liquid, of a substance which makes the coacervate richer in colloid (" condensing action). It then appears that the surface of the drop moves towards the side where this condensation (with possibly local form ation of small vacuoles as a consequence) is the most pronounced. As a consequence of this the whole contents of the coacervate drop are set in motion as can be seen from the motion of the vacuoles transported with it (Fig. 19a). 

Microscope appearance. Place a small amount of dry starch on a microscope slide, add a drop of water, cover with a slip and examine under the microscope. Characteristic oval grains are seen which have concentric rings round a hilum which is towards one end of the grain. Run a drop of very dilute iodine solution under the slip from a fine dropping-tube the grains become blue. 

A piece of the crumb of the size of a pin s head is moistened on a microscope slide with a drop of water and covered with a cover-slip, which is carefully pressed and turned round and round with the tip of the finger. In this way those starch granules which have undergone but little alteration are separated and moved towards the outer part of the preparation, where they may be easily observed. Thus were obtained the preparations for the microphotographs 33 and 34 of Plate V (at end of chapter) both were obtained from pure wheaten bread, the former being from a loaf made from 80% flour (i.e., flour containing 80% of the grain) and the latter from a small fancy loaf. 

When a light microscope is used to look at a wheat flour particle under water, practically no protein structure is discernible (Fig. 15.44, la). If the particle is stretched in one direction by moving the slide cover glass against the microscope slide, numerous protein strands with inserted starch granules become visible. These strands are... 

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