detected in the blood by Millon, and in the bile
by Weber. Silica reaches us in our vegetable
food, particularly in salad plants and cereal
grasses. After a haystack has been burnt
down, there is often found a sort of rough
glass at the bottom of the charred heap.
Philosophers have suggested that the stack
was consumed by lightning, and the falling
aerolite molten. Practical farmers have
hinted at an incendiary with matches in a
glass bottle. But the botanist refers to the
silica contained in the hay and wheat, and
shows that it is this which has been molten
by the fire into flint-glass.

The analogues of human hair are birds'
feathers, and silica is here found plentifully;
most plentifully in the wing-feathers, where
strength is required for purposes of flight.
If, like Coriolanus, we could have "no softer
cushion than the flint," it would be in the
form of feathers that the stony pillow would
be most acceptable.

Of magnesia we have but little to say.
It is always found in the human body. But
what it does there, and why it is there,
and in what precise form, are questions
not yet clearly answered. Probably
magnesia has the same qualities as potash and
sodium, and does their work occasionally,
when from an ill-selected diet these
are absent from the body without leave.
The dietetic relation of magnesia has been
made famous by its discovery in oats. You
could with difficulty form an idea of the
ecstasy of that happy Gael who achieved this
brilliant result. It appears that the acute
minds of certain Scotch philosophers, long
oppressed by the sense of the mental and
physical superiority of their race, had been
baffled in investigating its cause. They
could find no satisfactory scientific explanation
of the pre-eminence of the men on the
north of the Tweed over the degenerate
Southron, the puzzling difference 'twixt
Tweed-ledum and Tweed-ledee; but at last
this patriotic Scot announced that it was all
accounted for by the quantity of magnesia
which he eats in his oatcake. Probably those
who admit the fact will not cavil at the
explanation. A parallel speculation—which, we
believe, claims an American origin—goes to
show that differences in race and colour spring
from varieties in elements of food, and that
although it may be impossible to wash a
blackamoor white, it might be possible to feed
him white. These are philosophic bubbles,
blown but to burst.

There remains a mineral beyond all others
essential to life. If we may be permitted
to recal the very common phrase by which
man is said to be a brick, we would indicate
the propriety of speaking of phosphate of
lime as the mortar which completes the
edifice. The phosphate of lime cements and
stiffens the gelatine of the bones. It is the
so-called bone-earth, to which the bones owe
their stiffness and solidity. It is the
phosphate of lime which renders them capable of
supporting the weight of the body, protecting
the delicate organs of life, and serving as
levers on which the muscles may act.
Phosphate of lime reaches us in all flesh, and in
most articles of vegetable food, but especially
in some of the cereals. A striking illustration
of the value of phosphate of lime, as a
constituent of our dietary, may be found in
the fact that, nearly all the nations of the
earth feed either on wheat or rye, or on
barley or oats, and these grains appear to be
specially adapted for human use, by reason of
the large quantities of phosphate of lime
which they contain. There is plenty of
phosphate of lime in soups, and this may be a useful
way of getting at this mineral, where there
is a deficiency in the system.— For this
phosphate is a necessary constituent of all the
soft tissues and fluids of the body,—of cartilage,
muscle, milk, blood, of gastric and
pancreatic juices. In all these it is not mechanically
dissolved or deposited, but is so united
with their inmost structural elements, that it
is difficult to isolate it. Lehmann thinks it
obvious that this substance plays an important
part in the metamorphoses of the animal
tissues, and especially in the formation and
subsequent changes of the animal cells. But
it is in bone that phosphate of lime plays the
most important part. It forms more than
one-half of the entire osseous mass; its
proportions being nicely adjusted to the
exigences of each part. In the skull—which
guards the brain, the centre of the nervous
system, the core and kernel of our life—the
proportion of bone-earth amounts to sixty-seven
per cent.; the defences here are
strengthened, while in less important parts
the per centage falls to forty-five. The
law of its deposition may be stated thus:
—Bone-earth is added in proportion to the
thinness of the plate of bone to be strengthened,
or the importance of the organ to be
protected. When the natural balance is
disturbed, when the phosphate of lime is
insufficiently supplied or assimilated, a dreadful
disease occurs, called rickets, which is
characterised by bending of the bones, hideous
deformity, pressure on, and destruction of,
important organs, and, finally, death. The
cure for this condition of bone is medicine
containing the deficient ingredient—
phosphate of lime. Bones which do not contain
this substance are flexible; in fact, they
are only gelatine remains. In the dentine of
teeth we find sixty-six per cent. of phosphate
of lime; in the enamel nearly ninety per
cent.

But the mineral ingredients may not too
greatly encroach upon organic structures; for,
even here, death most often seizes upon those
bones, which being most stiff, with phosphate
of lime, have the most earthy taint. Life is a
constant battle between the dead matter of
earth, which strives continually to free itself
from the tyranny of organic laws, and the