It is then fed regularly to the fire by some mechanism. In the Roney stoker coal is carried to the fire on a series of connected rocker-bars, arranged on an incline. In another common furnace the coal is pushed down the inclined sides of the furnace by an oscillating pushing-bar. The advantages of a mechanical stoker are that coal is fed more uniformly, smoking is decreased, a lower grade of coal can be used with advantage and hand-labor is saved. Mechanical stokers are to-day used in many large stationary furnaces.
Stoke-upon-Trent, a manufacturing town in Staffordshire, England, on Trent River. It is a modern town noted for its factories of porcelain, earthenware, tiles and tessellated pavements, which are among the largest in the world. Coal-mining, bricklaying and iron-works are also carried on. There are statues of Wedgwood and Minton in the city. Population 89,015. See Borough of Stoke-upon-Trent by Ward.
Stolon (stō′lŏn), a branch especially adapted for propagation, as in the ordinary houseleek. The houseleek, surrounded by its stolons, each bearing a young plant at its tip, is sometimes called “hen and chickens.” An equivalent word is “offset.”
Stom′ach, an organ of digestion, present in some form in all animals above the sponges, with the exception of a few degenerated parasites. It is merely a receptacle for the food, and is provided with glands which secrete a digestive fluid. Digestion however, is carried farther and completed in the intestine and, therefore, the stomach is not the sole organ of digestion. The stomach of the human body is a sac on the left side just below the diaphragm. It has four coats: an outer, firm, serous coat; a muscular coat, with fibers arranged in longitudinal, transverse and oblique directions; a coat of loosely woven fibrous tissue; and an inner, mucous coat. The glands which secrete the gastric juice are derived from the latter coat. There are two varieties, those nearer the heart, called cardiac glands, and those at the other end of the stomach where the intestine is joined, called the pyloric glands. The latter are the more important. The stomach is under control of the nervous system, both as to its movements and as to the secretion of gastric juice. When food is introduced into the stomach, the secretion of gastric juice is stimulated through the nervous system. The gastric juice contains a ferment called pepsin, which acts especially on proteids like lean meat, white of eggs, gluten of bread etc. This action takes place in the presence of acid, and in the glands are certain cells which provide hydrochloric acid in small amount. When this is deficient, grave stomach disorders arise. The food is reduced to a condition called chyme and is passed on into the intestine. The object of digestion is to render food soluble that it may pass by absorption through the walls of the stomach and intestine. This is not a process depending upon life, as it can be performed with artificial gastric juice outside the body. The characteristic action of the gastric juice is upon proteids, while the pancreatic juice, which is introduced into the intestine, is a universal digester, of greater efficiency than the gastric juice. It aids in the digestion of starches and fats as well as in completing that of the proteids.
Stomata (stŏm′ȧ-tȧ) (in plants). Narrow
openings are developed in the epidermis of
STOMATA AND LEAF
all aërial parts
of plants which
require and
emit gases.
(See
Aëration.)
Gaseous exchanges
especially
abound in
green tissues;
hence stomata
are chiefly
displayed by the
foliage-leaves
of the higher
plants. Each
stoma consists
of two specially
organized
epidermal
cells, called
guard-cells,
which are
crescentic in surface-view and, being in
contact by their concave faces, leave a
lens-shaped opening between them. This
opening leads into the system of intercellular
passageways among the working-cells,
and thus provides for a free exchange of
gaseous substances between the working-cells
and the outside air. The guard-cells
change form with the varying amounts of
moisture in the air, and so regulate the size
of the opening between them. Stomata
have been called “automatic gateways” on
account of this peculiar power of the guard-cells.
See Leaf and Transpiration.
Stone-Age is a term used to designate a stage of culture in man's development, not a chronological period in geological history. It refers to the period among any people when the use of metals is unknown or, if known at all, does not involve the knowledge of smelting. At such a time stone is largely used in making implements and tools, though other materials, as wood, bone and shell are also employed. The stone age is known to have existed in Europe many hundreds of years ago; in North America it continued among the Indians until the 18th century; in some other places it probably exists at the present time.
