Common objects of the microscopeWood, J. G. (John George)
Science
Common objects of the microscope
Wood, J. G. (John George)
Microscopes; Microscopy
We will now glance at the examples of starch which are given in the
Plate, and which are a very few out of the many that might be figured.
Fig. 2 represents the starch of wheat, the upper grain being seen in
front, the one immediately below it in profile, and the two others
being examples of smaller grains. Fig. 6 is a specimen of a very minute
form of starch, where the granules do not seem to advance beyond
their earliest stage. This specimen is obtained from the parsnip; and
although the magnifying power is very great, the dimensions of the
granules are exceedingly small, and except by a very practised eye they
would not be recognisable as starch grains.
Fig. 3 is a good example of a starch grain of wheat, exemplifying the
change that takes place by the combined effects of heat and moisture.
It has already been observed that cold water exercises little, if
any, perceptible influence upon starch; but it will be seen from
the illustration that hot water has a very powerful effect. When
subjected to the action of water at a temperature over 140° Fahr.,
the granule swells rapidly, and at last bursts, the contents escaping
in a gelatinous mass, and the external membrane collapsing into the
form which is shown in Fig. 3, which was taken out of a piece of hot
pudding. A similar form of wheat starch may also be detected in bread,
accompanied, unfortunately, by several other substances not generally
presumed to be component parts of the “staff of life.”
In Fig. 7 are represented some grains of starch from West Indian
arrowroot, and Fig. 8 exhibits the largest kind of starch grain known,
obtained from the tuber of a species of canna, supposed to be _C.
edúlis_, a plant similar in characteristics to the arrowroot. The
popular name of this starch is “Tous les Mois,” and under that title
it may be obtained from the opticians, or chemists.
Fig. 10 shows the starch granules from Indian corn, as they appear
before they are compressed into the honeycomb-like structure which
has already been mentioned. Even in that state, however, if they are
treated with iodine, they exhibit the characteristics of starch in a
very perfect manner. Fig. 11 is starch from sago, and Fig. 12 from
tapioca, and in both these instances the several grains have been
injured by the heat employed in preparing the respective substances for
the market.
Fig. 13 exhibits the granules obtained from the root of the water-lily,
and Fig. 14 is a good example of the manner in which the starch
granules of rice are pressed together so as to alter the shape and
puzzle a novice. Fig. 16 is the compound granule of the oat, which
has already been mentioned, together with some of the simple granules
separated from the mass; and Fig. 15 is an example of the starch grains
obtained from the underground stem of the horse-bean. It is worthy of
mention that the close adhesion of the rice starch into those masses is
the cause of the peculiar grittiness which distinguishes rice flour to
the touch.
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