In vivo.

Experiments performed in a living organism.

In vivo means in the living, and refers to studies conducted in whole living organisms, which in preclinical peptide research usually means rodents and occasionally larger animals. The advantage over in vitro work is that the compound now has to survive administration, distribute through the body, avoid being cleared before it arrives, and produce its effect in the presence of every other system that is running at the same time, including the immune system, hormonal feedback loops, and normal healing processes. That is a much more demanding test, and many compounds that look excellent in a dish do nothing in an animal. Interpretation still requires care. The species matters, because rodent physiology, metabolic rate, healing speed, and lifespan differ from human equivalents in ways that are directly relevant to metabolic and repair research. The model matters, because an artificially induced injury or a genetically engineered disease state is a simplified stand-in for the human condition it represents. And the amounts used, scaled for body size, are often much larger than any human exposure. The misunderstanding worth correcting is that in vivo means in humans. It does not; unless the study says human subjects, it almost always means animals.