This is effected by the action of warmth, moisture, and a ferment
in the seed. Glucose is soluble and is at first the plant's main
food.

Commercial starch is made in the United States chiefly from corn;
in Europe, from potatoes. Differences in the size of starch
granules enable microscopists to determine the plant to which
they belong.

324. Cellulose, or woody fiber, is the basis of all vegetable
cell walls. Cotton fiber represents almost pure cellulose. From
it are made paper and woven tissues. In paper manufacture, woody
fiber is made into a pulp, washed, bleached, filtered, hot-
pressed, and sometimes glazed. Parchment paper, vegetable
parchment, is made by dipping unglazed paper for half a minute
into cold dilute H2SO4, 1 part H2O, 2 1/2 parts H2SO4, and then
washing. The fiber, by chemical change, is thus toughened. The
cell walls of wood are impure cellulose; hence the inferior
quality of paper made from wood-pulp. Paper is now employed for a
large number of purposes for which wood has heretofore been used,
such as for barrels, pails, and other hollow ware, wheels,
etc.

325. Gun-cotton is made by treating cotton fiber with H2SO4
and HNO3, washing and drying. To all appearances no change has
taken place, but the substance has become an explosive compound.

326. Dextrin, a gummy substance used for the backs of postage
stamps, is a carbo-hydrate, as in fact are gums in general.
Dextrin is made by heating starch with H2SO4 at a lower
temperature than for dextrose.

327. Zylonite and Celluloid. -These two similar substances embody
the latest use of cellulose in manufactured articles. For
zylonite, linen paper is cut into strips two feet by one inch,
soaked ten minutes in a mixture of H2SO4 and HNO3, a process
called nitration, washed for several hours, then ground to a fine
pulp, and thoroughly dried. It is then similar to pyroxiline.
Aniline coloring-matter of any desired shade is added, after
which it is dissolved by soaking some hours in alcohol and
camphor, the liquid is evaporated, and the substance is kneaded
between steam-heated iron rollers, dried with hot air, and
finally subjected to great pressure, to harden it, and cut into
sheets. Zylonite is combustible at a low temperature, and when in
the pyroxiline stage, explosively so. Ivory, coral, amber, bone,
tortoise shell, malachite, etc., are so closely imitated that the
imitation can only be detected by analysis. Collars, combs,
canes, piano-keys, and jewelry, are manufactured from it, and it
can be made transparent enough for windows.

 CHAPTER LIX

CHEMISTRY OF FERMENTATION.

328. Ferments.--A large number of chemical changes are brought
about through the direct agency of bodies called ferments; their
action is called fermentation. Ferments are sometimes lifeless
chemical products found in living bodies; but in other cases they
are humble plants.

329. Yeast is one of the most common of living ferments, wild
yeast being a microscopic plant found on the ground near apple-
trees and grape-vines, and often in the air. The cultivated
variety is sold by grocers. The temperature best suited to the
rapid multiplication of the germs forming the ferment plant is 25
degrees to 35 degrees.

330. Alcoholic and Acetic Fermentation.--The changes which the
juice of the apple undergoes in forming cider and vinegar are a
good illustration of fermentation by a living plant. Apple-juice
contains sucrose. Yeast germs from the air, getting into this
unfermented liquor, cause it to "work." This process changes
sucrose to glucose, and glucose to alcohol and CO2, and is known
as alcoholic fermentation. The latter reaction, C6H12O6 = 2 C2H6O
+ 2 CO, is only partially correct, as other products are formed.
The juice has now become cider; the sugar alcohol. After a time,
if left exposed, another organism finds its way to the alcohol,
and transforms it into acetic acid, HC2H8O2, and H2O. This
process is called acetic fermentation. C2H6O + O2 = HC2H3O2 +
H2O. For this fermentation, a liquor should not have over ten per
cent of alcohol. Mother of vinegar consists of the germs that
caused the fermentation. Still a third species of ferment may
cause another action, changing acetic acid to H2O and CO2. The
vinegar then tastes flat. HC2H3O2 + 4 O = 2H2O + 2 CO2.

Some mineral acids, as H2SO4 and HCl, and some organic acids, are
regarded as lifeless ferments. To this class are thought to
belong the diastase of malt and the pepsin of the stomach. This
variety of ferments exists in the seeds of all plants, and
changes starch to glucose.

331. Bread which is raised by yeast is fermented, the object
being to produce CO2, bubbles of which, with the alcohol, cause
the dough to rise and make the bread light.

Grapes and other fruits ferment and produce wines, etc., from
which distilled liquors are obtained.

332. Lactic Fermentation changes the sugar of milk, lactose, to
lactic acid, i.e. sour milk. In canning fruit, any germs present
are killed by heating, and those from the air are excluded by
sealing the can. Milk has been kept sweet for years by boiling,
and tightly covering the receptacle with two or three folds of
cotton cloth.

333. Putrefaction is fermentation in which the products of decay
are ill-smelling. Saprophytes attack the dead matter, feed on it,
and cause it to putrefy. This action, as well as that of ordinary
fermentation, used to be attributed solely to oxygen. Germs bring
back organic matter to a more elementary state, and so have a
very important function. By some scientists, digestion is
regarded as a species of fermentation, probably due to the action
of lifeless ferments; e.g. sucrose cannot be taken into the
system, but is first fermented to glucose.

334. Most Infectious Diseases are now thought to be due to
parasites of various kinds, such as bacteria, microbes, etc.,
with which the victim often swarms, and which feed on his
tissues, multiplying with enormous rapidity. Such diseases are
small-pox, intermittent and yellow fevers, etc. Consumption, or
tuberculosis, is believed to be caused by a microbe which
destroys the lungs. In some diseases not less than fifteen
billions of the organisms are estimated to exist in a cubic inch.
These multiply so rapidly that from a single germ in forty-eight
hours may be produced nearly three hundred billions. These germs
do not spring into life spontaneously from inorganic matter, but
come from pre-existent similar forms. Parasites are not so rare
in the system even of a healthy person as is generally supposed.
They are found on our teeth and in many of the tissues of the
body.

Several infectious diseases are now warded off or rendered less
virulent by vaccination, the philosophy of which is that the
organisms are rendered less dangerous by domestication; several
crops, or generations, are grown in a prepared liquid, each less
injurious than its parent. Some of the more domesticated ones are
introduced into the system, and the person has only a modified
form of the disease, often scarcely any at all, and is for a more
or less limited time insured against further danger.

Dust particles and motes floating in the air are in part germs,
living or dead, often requiring only moisture and mild
temperature for resuscitation. Most of these are harmless.

Chapter LX.

CHEMISTRY OF LIFE.

335. Growth.--The chemistry of organic life is very complex, and
not well understood. A few of the principal points of distinction
between the two great classes of living organisms, plants and
animals, are all that can be noted here. Minerals grow by
accretion, i.e. by the external addition of molecules of the same
material as their interior. A crystal of quartz grows by the
addition of successive molecules of SiO2, arranged in a
symmetrical manner around its axis. The growth of crystals can be
seen by suspending a string in a saturated solution of CuSO4, or
of sugar. In plants and animals the growth is very much more
complex, but is from the interior, and is produced by the
multiplication of cells. To produce this cell-growth and
multiplication, food-materials must be furnished and assimilated.
In plants, sap serves to carry the food-materials to the parts
where they are needed. In the higher animals, vari- ous fluids,
the most important of which is the blood, serve the same purpose.

336. Chemistry of Plants.--In ultimate analysis, plants consist
mainly of C, H, O, N, P, K. In proximate analysis, as it is
called, they are found to contain these elements combined to form
substances like starch, sugar, etc. Water is the leading compound
in both animals and plants. One of the most important differences
between animals and plants is, that all plants, except parasitic
ones, are capable of building up such compounds as starch from
mineral food-stuffs, while animals have not that power, but must
have the products of proximate analysis ready prepared, as it
were, by the plant. Hence plants thrive on minerals, whereas
animals feed on plants or on other animals. The power which
plants have of transforming mineral matter is largely due to
sunlight, the action of which in separating CO, was described.
The reaction in the synthesis of starch from CO2 and H2O in the
leaf, is thought to be as follows: 6 CO2 + 5 H2O = C6H10O5 + 12
O. C6H10O5 is taken into the tree as starch; 12 O is given back
to the air. All the constituents, except CO2 and a very small
quantity of H2O, are absorbed by the roots, from the soil, from
which they are soon withdrawn by vegetation. To renew the supply,
fertilizers or manures are applied to the soil. These must
contain compounds of N, P, and K. N is usually applied in the
form of ammonium compounds, e.g. (NH4)2SO4, (NH4)2CO3, and
NH4NO3. The reduction and application of Cas(PO4)2 for this
purpose was described. K is usually applied in the form of KCl
and K2SO4.

337. Food of Man.--In the higher animals the object is not so much
to increase the size as to supply the waste of the system. The
principal elements in man's body are C, H, O, N, S, P.

An illustration of the transformation of mineral foods by plants

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