If dried starch grains are rubbed between two glass plates, the grains
will be seen under the microscope to be fissured, and if then wetted and
filtered, the filtrate will be a perfectly clear liquid showing a strong
starch reaction with iodine. Since no solution is obtained from uninjured
grains, even after soaking for weeks in water, Brukner concludes that the
outer layers of the starch grains form a membrane protecting the interior
soluble layers from the action of the water.

The soluble filtrate from starch paste also contains a substance identical
with granulose. Between the two kinds of starch, the granular and that
contained in paste, there is no chemical but only a physical difference,
depending on the condition of aggregation of their micellæ.

W. Nageli maintains that granulose, or soluble starch, differs from
amylodextrin in the former being precipitated by tannic acid and acetate
of lead, while the latter is not. Brukner fails to confirm this
difference, obtaining a voluminous precipitate with tannic acid and
acetate of lead in the case of both substances. Another difference
maintained by Nageli, that freshly precipitated starch is insoluble,
amylodextrin soluble in water, is also contested; the author finding that
granulose is soluble to a considerable extent in water, not only
immediately after precipitation, but when it has remained for twenty-four
hours under absolute alcohol. Other differences pointed out by W. Nageli,
Brukner also maintains to be non-existent, and he regards amidulin and
amylodextrin as identical. Brucke gave the name erythrogranulose to a
substance nearly related to granulose, but with a stronger affinity for
iodine, and receiving from it not a blue but a red color. Brukner regards
the red color as resulting from a mixture of erythrodextrin, and the
greater solubility of this substance in water.