OSMOSIS—The process of diffusion between fluids of different molecular pressures.
SPORE FORMATION—A mode of reproduction in lower forms of life by which resistant bodies, spores, are formed. These have many analogies with the seed of higher plants.
SYMBIOSIS—A mutual adaptation between parasite and host.
TRANSUDATION—The normal interchange of fluid between the blood and the tissue fluids. The material interchanged is the transudate.
TROPISM—The influence of forces which direct the movement of cells.
ULTRA-MICROSCOPE—A form of microscope which by means of oblique illumination renders visible objects so small as to be invisible with the ordinary microscope.
VIRUS—A substance either living or formed by living things which may cause disease.