A Book of Natural History | Page 5

of animal
and vegetable bodies, but that every animal and every plant, at all
periods of its existence, contains one or other of them, though, in other
respects, the composition of living bodies may vary indefinitely. Thus,
some plants contain neither starch nor cellulose, while these substances
are found in some animals; while many animals contain no horny
matter and no gelatin-yielding substance. So that the matter which

appears to be the essential foundation of both the animal and the plant
is the proteid united with water; though it is probable that, in all
animals and plants, these are associated with more or less fatty and
amyloid (or starchy and saccharine) substances, and with very small
quantities of certain mineral bodies, of which the most important
appear to be phosphorus, iron, lime, and potash.
Thus there is a substance composed of water + proteids + fat +
amyloids + mineral matters which is found in all animals and plants;
and, when these are alive, this substance is termed protoplasm.
The wheat plant in the field is said to be a living thing; the fowl
running about the farmyard is also said to be a living thing. If the plant
is plucked up, and if the fowl is knocked on the head, they soon die and
become dead things. Both the fowl and the wheat plant, as we have
seen, are composed of the same elements as those which enter into the
composition of mineral matter, though united into compounds which do
not exist in the mineral world. Why, then, do we distinguish this matter
when it takes the shape of a wheat plant or a fowl, as living matter?
In the spring a wheat-field is covered with small green plants. These
grow taller and taller until they attain many times the size which they
had when they first appeared; and they produce the heads of flowers
which eventually change into ears of corn.
In so far as this is a process of growth, accompanied by the assumption
of a definite form, it might be compared with the growth of a crystal of
salt in brine: but, on closer examination, it turns out to be something
very different. For the crystal of salt grows by taking to itself the salt
contained in the brine, which is added to its exterior; whereas the plant
grows by addition to its interior: and there is not a trace of the
characteristic compounds of the plant's body, albumin, gluten, starch,
or cellulose, or fat, in the soil, or in the water, or in the air.
Yet the plant creates nothing; and, therefore, the matter of the proteins
and amyloids and fats which it contains must be supplied to it, and
simply manufactured, or combined in new fashions, in the body of the
plant.

It is easy to see, in a general way, what the raw materials are which the
plant works up, for the plant get nothing but the materials supplied to it
by the atmosphere and by the soil. The atmosphere contains oxygen
and nitrogen, a little carbonic acid gas, a minute quantity of
ammoniacal salts, and a variable proportion of water. The soil contains
clay and sand (silica), lime, iron, potash, phosphorus, sulphur,
ammoniacal salts, and other matters which are of no importance. Thus,
between them, the soil and the atmosphere contain all the elementary
bodies which we find in the plant; but the plant has to separate them
and join them together afresh.
Moreover, the new matter, by the addition of which the plant grows, is
not applied to its outer surface, but is manufactured in its interior; and
the new molecules are diffused among the old ones.
The grain of wheat is a part of the flower of the wheat plant, which,
when it becomes ripe, is easily separated. It contains a minute and
rudimentary plant; and, when it is sown, this gradually grows, or
becomes developed into, the perfect plant, with its stem, roots, leaves,
and flowers, which again give rise to similar seeds. No mineral body
runs through a regular series of changes of form and size, and then
gives off parts of its substance which take the same course. Mineral
bodies present no such development, and give off no seeds or germs.
They do not reproduce their kind.
The fowl in the farmyard is incessantly pecking about and swallowing
now a grain of corn, and now a fly or a worm. In fact, it is feeding, and,
as every one knows, would soon die if not supplied with food. It is also
a matter of every-day knowledge that it would not be of much use to
give a fowl the soil of a cornfield, with plenty of air and water, to eat.
In this respect, the fowl is like all