Plaice

3750

Planet

Rucker, of the U. S, Public Health Service,
puts it, 'Plague is primarily a disease of ro-
dents, and secondarily and accidentally a
disease of man.' It was P. L. Simond who
first suggested, in 1899, that the flea fur-
nished the medium hy which bubonic plague
is transmitted from rat to rat and from rat
to man. Several different vaccines are in use
which exert an important effect in the reduc-
tion of the mortality from plague, and which
furnish a valuable adjunct to sanitary pre-
ventive measures.

Plaice, (Pleuronedes platessa), a valuable
European flat-fish, distinguished by the eyes
being on the right side, red spots on the upper
surface, and bony tubercles behind the eyes.
It may exceed thirty inches in length, though
usually it measures less than 2 ft., and weighs
from 8 to 10 pounds. The plaice is found
from the Bay of Biscay to the n. coast of
Europe, and is abundant in moderately deep
and shallow water at Iceland and around the
British Isles.

Plain, a land surface which approximates
to a plane. As a rule, the term is confined to
such flat surfaces as are found in the low-
lands. The higher plains are generally table
lands or plateaus, but the great plains of North
America rise almost imperceptibly from sea
level to 6,000 ft. The interruption of moun-
tain ranges or steep escarpments rather than
mere elevation delimits the plain. Plains may
be due to denudation or accumulation. Marine
plains are old sea floors now above sea level,
such as the Atlantic and Gulf coastal plains of
North America.

Plainfield, city, New Jersey, 24 not. s.w. of
New York City. It is a residential city with
considerable industrial interests. The pictur-
esque First Mountain, a continuation of Or-
ange Mountain, lies on the n.w. Manufactures
include auto trucks, newspaper presses, silk,
silk hosiery, women's dresses, pneumatic
tubes, concrete machinery and machine tools.
Hundreds of New York business men live in
Plainfield, which has express service on the
Central Railroad of New Jersey; p.37469.

Plains of Abraham, hills s,w. of Quebec.
See ABRAHAM* HEIGHTS op,

Plain-song, Plain-chant, Gregorian
Chant, or Gregorian Music, terms for an
ancient unmeasured form of sacred music set
to passages contained in Holy Writ, and used
in the service of the Church since the begin-
ning of the Christian era. Its distinguishing
points are its recitative-like character, the
modes, or scales, in which it is written, which
are more numerous and varied than the mod-

ern major and minor; and its being (orig-
inally) sung in unison. The cultivation of
plain-song has received great impetus from
the instructions on church music given to the
Roman Catholic Church by Pius x. in 1903,
in which he strongly advocated the use of
Gregorian music.

Plaintiff, a person in whose name a civil
action is commenced. He may be acting in
his individual or a representative capacity,
as where one sues as trustee. In some States
of the United States, one who maintains an
action in equity is known as the complainant.

Planarian, a term which may be applied to
practically all the members of the class Tur-
bellaria, a division of Platyhelminthes, or
flat-worms. Planarians are small, oval, or
elliptical, leaf-life creatures which are al-
most all free-living, and which are found in
the sea, in fresh water, and occasionally in
damp earth.

Planchette, a piece of board shaped like
a heart, mounted on supports, two of which
are casters fixed at the broader end, with a
pencil at the other, so that it moves easily
over a sheet of paper when hands are placed
lightly on it. This instrument was at one
time believed to write independently of the
volition of the person touching it; but its
action is now explained by the 'dominant
idea/ which influences the hands of the oper-
ator. See OUIJA BOARD.

Planson, Pol-Henri (1854-1914), French
operatic singer, was born in Fumay, France.

Plane Geometry deals with the properties
of co-planar lines and points; but the theory
of planes themselves belongs to the geometry
of space, also called solid geometry. Geometry
tells us that we completely determine a plane
when we know on it (i) two intersecting
straight lines, or (2) one line and a point
without it, or (3) three non-collincar points,
or (4) two parallel lines (not necessarily
straight lines). It will be observed that a
plane has only two dimensions—length and
breadth, whereas a solid has three—length,
breadth, and depth; a line, one only—length;
and a point, none.

Planet, so called in contradistinction to a
'fixed* star, is an opaque body, permanently
revolving round the sun at a distance of
from 186 million to some four billion m. The
ancients knew five planets:—Mercury, Ve-
nus, Mars, Jupiter and Saturn. Modern as-
tronomers have added the Earth, Uranus,
Neptune and Pluto, making nine in all. Sec-
ondary planets arc the satellites, or bodies
that revolve around the primary planets,