Microbial Viability: Ability of a microbe to survive under given conditions. This can also be related to a colony's ability to replicate.Cell Survival: The span of viability of a cell characterized by the capacity to perform certain functions such as metabolism, growth, reproduction, some form of responsiveness, and adaptability.Fetal Viability: The potential of the FETUS to survive outside the UTERUS after birth, natural or induced. Fetal viability depends largely on the FETAL ORGAN MATURITY, and environmental conditions.Tissue Survival: The span of viability of a tissue or an organ.Apoptosis: One of the mechanisms by which CELL DEATH occurs (compare with NECROSIS and AUTOPHAGOCYTOSIS). Apoptosis is the mechanism responsible for the physiological deletion of cells and appears to be intrinsically programmed. It is characterized by distinctive morphologic changes in the nucleus and cytoplasm, chromatin cleavage at regularly spaced sites, and the endonucleolytic cleavage of genomic DNA; (DNA FRAGMENTATION); at internucleosomal sites. This mode of cell death serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth.Cells, Cultured: Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.Cell Line, Tumor: A cell line derived from cultured tumor cells.Cryopreservation: Preservation of cells, tissues, organs, or embryos by freezing. In histological preparations, cryopreservation or cryofixation is used to maintain the existing form, structure, and chemical composition of all the constituent elements of the specimens.Cell Proliferation: All of the processes involved in increasing CELL NUMBER including CELL DIVISION.Tetrazolium Salts: Quaternary salts derived from tetrazoles. They are used in tests to distinguish between reducing sugars and simple aldehydes, for detection of dehydrogenase in tissues, cells, and bacteria, for determination of corticosteroids, and in color photography. (From Mall's Dictionary of Chemistry, 5th ed, p455)Time Factors: Elements of limited time intervals, contributing to particular results or situations.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Cell Death: The termination of the cell's ability to carry out vital functions such as metabolism, growth, reproduction, responsiveness, and adaptability.Cell Line: Established cell cultures that have the potential to propagate indefinitely.Dose-Response Relationship, Drug: The relationship between the dose of an administered drug and the response of the organism to the drug.