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Modern science offers a variety of methods for the safe experimentation and efficacy testing of samples and products. Testing methods in science are traditionally called by their Latin names, such as in vitro, in vivo, ex vivo, and in silico. Each name broadly describes the test environment: for instance, in vivo and ex vivo mean, experiments conducted inside and outside a living body, respectively. The basic difference between the above four is that all apart from in vivo involve experiments that take place outside of a living organism, but there are also important differences between them all. Below we analyse the differences between the four methods of undertaking scientific experiments.
In vitro
In vitro translates from Latin as “in glass.” This testing method involves experiments on biological matter (cells or tissues) outside of a living organism. The reference to glass is quite literal: in vitro experiments were historically conducted in a glass Petri dish. In vitro experiments can be conducted on a wide range of test subjects, from bacteria to cells derived from living organisms. Thanks to modern science, increasingly complex in vitro models are now available. Anything from modified bacteria to reconstructed tissues can be created, modified and reproduced many times, especially for the needs of the experiment.
In vivo
In vivo, Latin for “within the living”, refers to experimentation using a whole, living organism as opposed to a partial or dead organism. Animal studies and clinical trials are two forms of in vivo research. In vivo testing is often employed over in vitro because it is better suited for observing the overall effects of an experiment on a living subject. While there are many reasons to believe in vivo studies have the potential to offer conclusive insights about the nature of medicine and disease, there is a number of ways that these conclusions can be misleading. For example, a therapy can offer a short-term benefit, but long-term harm.
Ex vivo
Ex vivo original Latin meaning is “outside of the living”. means that which takes place outside an organism. In science, ex vivo refers to experimentation or measurements done in or on tissue in an artificial environment outside the living organism with the minimum alteration of natural conditions. Ex vivo conditions allow experimentation under more controlled conditions than is possible in vivo experiments (in the intact organism), at the expense of altering the “natural” environment. The term ex vivo is often differentiated from the term in vitro (“within the glass”) in that the tissue or cells need not be in culture; these two terms are not synonymous. In cell biology, ex vivo procedures often involve living cells or tissues taken from an organism and cultured in a laboratory apparatus, usually under sterile conditions with no alterations for up to 24 hours. Experiments lasting longer than this using living cells or tissue are typically considered to be in vitro.
In silico
In silico is an expression used to mean “performed on computer or via computer simulation.” The expression in silico was first used in public in 1989 in the workshop “Cellular Automata: Theory and Applications” in Los Alamos, New Mexico. Pedro Miramontes, a mathematician from National Autonomous University of Mexico (UNAM), presented the report “DNA and RNA Physicochemical Constraints, Cellular Automata and Molecular Evolution.” In his talk, Miramontes used the term “in silico” to characterize biological experiments carried out entirely on a computer. Although in silico studies represent a relatively new avenue of inquiry, it is commonly used widely in drug discovery and development studies, where it predicts how drugs interact with the body and with pathogens.
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