The Latin terms in vitro and in vivo began appearing in the medical literature around the turn of the 20th century, as the scientific revolution in medicine gathered pace. Directly translated as “in glass” and “in life”, they distinguish biological processes conducted in the laboratory from those occurring within a living organism. An antibiotic, for example, might kill bacteria in the Petri dish yet fail to cure infections in human patients. A drug might interrupt degenerative changes in nerve cells grown in tissue culture but cause unacceptable side effects if administered as a treatment for dementia. In vitro findings are the engine of research, but it is in vivo outcomes that ultimately matter.
In vitro fertilisation is the instance most people will be familiar with. These days IVF seems commonplace, a routine if expensive option for couples unable to conceive naturally. Few now remember the collective bated breath that accompanied its first use by the fertility pioneers Patrick Steptoe and Robert Edwards in 1978. In vitro research had proved the process of life could be started in the lab, and animal models offered assurance that uneventful pregnancy, birth and normal child development should follow once embryos had been implanted in the womb. But until Louise Brown, the first “test-tube baby”, proved IVF was both possible and safe in humans, no one could be entirely certain the in vivo outcome would match the experimental promise.
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