PHYSIOLOGY

1487

PIASTER

the circulation, the secretion of substances like the digestive juices and other forms of secretions in the body; and the action of the liver, pancreas and similar organs. Respiration is connected with nutrition, because the oxygen brought in is used in all processes of the body, and the removal of the carbon dioxide (CO2) is an aid to nutrition. One must, therefore, learn all about the breathing organs and the nature of the exchanges between the blood, the air and the tissues. The living protoplasm of the body is continually undergoing disintegration; it breaks into carbon dioxide, water and nitrogenous compounds. In order that nutrition may be effectively carried on, these waste-products must be removed. This topic includes the action of the kidneys, the lungs and the skin The varied chemical changes in assimilating the food and the reverse set of changes resulting in the liberation of energy must be considered under nutrition.

Another great division of physiology deals with the means by which an animal or plant is brought into proper relation with its surroundings This in higher animals includes the action cf the nervous system and sense-organs as well as control of the nervous system over the organs. The muscles and organs of protection are also involved in bringing about a harmonious relation between surroundings and the animal. Finally, reproduction refers to the preservation of the race, and is more for the benefit of the race, generally speaking, than for the individual.

A study of all these varied activities is physiology. Reference must be made to text-books and manuals for further consideration. It is a common fault with our elementary physiologies to go too much into the discussion of the effects of alcohol and narcotics. The importance of such a discussion is unquestioned, but the facts of physiology and hygiene should stand out in unrivaled prominence. Among the smaller texts Huxley's Lessons in Elementary Physiology is the most lucid statement of the facts of physiology yet presented. Among the best books of greater extent may be mentioned Foster's Textbook of Physiology; Stewart's Manual of Physiology; Kirke's Handbook of Physiology; Howell's American Textbook of Physiology; Verworn's General Physiology; Martin's The Human Body; and Hall's Textbook of Physiology. It goes without saying that the most recent edition of each must be used. See Blood, Circulation, Heart, Liver, Muscle, Nerves, Respiration.                           Wm. A. Locy.

Physiology (of plants), that branch of science which treats of the activities of living beings. These essentially are the same in plants as in animals, but often are simpler. Plant physiology is concerned with the action of the plant body as a whole,

the part which each of its organs takes and the ways in which they are adjusted to one another and the external world. (See Ecology.) The work of a particular part or organ is called its function. The important general functions of plants are absorb-tion; water transfer; transpiration; nutrition (in the narrower sense) including digestion, photosynthesis and assimilation ; secretion; respiration; growth; and movement. (See these topics and Irritability.) In the higher plants the root is an absorbing organ for water, mineral salts and such organic matter as is soluble in water ; the root, stem and leaves are furnished with strands of tissues along which water and foods can travel readily; the leaves and the surface of the stem, at least when young, are organs of absorption and evolution of the gases carbon dioxide and oxygen; they also lose water by evaporation; and they are most important as organs for making carbohydrate foods. All these functions, however, may go on in a single cell of one of the simplest plants.

Pian'ofor'te, a stringed musical instrument played by keys, developed out of the clavichord and harpsichord. It differs from these chiefly in the introduction of hammers with which to put the strings in vibration, connected with the keys by a mechanism that enables the player to modify the intensity of the sound at will It is this peculiarity to which the name is due, piano being the Italian for soft and forte for loud. The strings are stretched across a compound frame of wood and metal, composed of bars, rods and strengtheners of various kinds. This framework includes a wooden sound-board. The mechanism by which hammers are connected with the keys is called the action of the instrument. The duration of a note is regulated by the damper. This consists of a piece of leather, resting on the top of the string and connected with the back part of the key by a vertical wire. When a key is pressed down, its damper is raised off the string so as to allow the sound to be clear and open; but when the finger is taken from the key, the damper wire falls immediately, and the damper presses down on the string, muffling and stopping the vibration. One of the pedals is called the loud, the other the soft pedal. Great difference of detail exists in the "actions" of different makes, but ail have the same essential parts. See Hopkins' Musical Instruments.

Piaster (pÔ-ăs'tĕr), "a plaster" in the Latin; in the Romance languages "anything spread out," "a plate," "a coin." The word is applied to an old Spanish coin, worth not quite $1.00 of United States money. It was divided into eight reals, and hence was called "a piece of eight." The Italian piaster is an imitation of and nearly equal to the Spanish piaster in value