Part 22

Protein. One of a class of complex organic substances consisting of carbon, hydrogen, nitrogen, oxygen, and, in some cases, other elements. All living cells contain proteins.

Protoplasm. The living matter of which all animal and plant cells are formed.

Protozoan. A member of the phylum (Protozoa) of animals of the simplest type. A one-celled animal.

Pseudo-. In many compounds, false, seeming, similar to.

Psychiatry. The treatment of mental disease.

Psychical research. The study of phenomena which are not considered by scientists as realities, and which are explained by some persons as due not to natural forces but rather to spirit as opposed to matter. If such phenomena are explained by means of the laws of physics and psychology, there is no need for special “psychical research.” There seems to be no reason why we should postulate spiritual or vital force, even if our knowledge is not yet sufficient to explain all phenomena scientifically.

Psychology. The study of the mind; in practice, the study of behavior. Literally: the science of the soul. Perhaps psychology is not yet a true science, but this branch of knowledge is undoubtedly becoming more scientific, in spite of strong philosophical and mystical tendencies.

Psychophysics. The study of the relation between the mental and the physical, between psychology and physics.

Psychosis. Mental derangement, especially when there is no apparent brain or nerve injury. Consciousness, a conscious process.

Pteridophyte. One of a phylum (Pteridophyta) of flowerless plants, including the ferns.

Pure. Unmixed, abstract. Pure science deals with general principles, not with particular applications.

Pyro-. In compounds, fire-, fever-.

Quantel. An elementary entity of matter consisting of positive and negative parts, moving in all directions with the velocity of light, capable of passing through solids. (According to the theory of Langmuir.)

Quantity. Anything which can be represented by means of a number. In chemistry, the number of gram molecules.

Quantum. The unit of energy transmitted by radioactive bodies.

Quaternary. Belonging to the most recent geological period.

Radical. Pertaining to a root, growing out of or from a point close to the root. An atomic group which remains unchanged during the ordinary reactions of the compound of which it is a part.

Radicle. That part of the embryo of a plant which develops into the main root. A rootlike subdivision of a nerve or vein. Sometimes a mere spelling variation of radical.

Radioactive. Emitting invisible rays that penetrate opaque matter and produce electrical effects. Radium and some other substances are especially radioactive, but radioactivity is supposed to be characteristic of all substances.

Radium. A metallic element. Symbol: Ra.

Rarefaction. Making less dense.

Ray. A line at right angles to the wave front in which various forms of energy may be transmitted.

React. Tend in the reverse direction, enter into chemical combination. Act because of a stimulus.

Reaction. An opposing force. A chemical change. The usual nervous response.

Real number. A number representing a quantity and one of two opposite directions or senses.

Réaumur. A thermometric scale with the boiling point of water at 80 degrees and the freezing point at zero.

Recapitulation Theory. The theory which was at one time generally favored by evolutionists, still accepted by many biologists, that ontogeny recapitulates phylogeny; i. e., that the development of the individual is an abridgement of the natural history of the species to which it belongs.

Recent. In geology, pertaining to the epoch still in existence.