Defensive and nutritive Qi wèi qì · yíng qì · 卫气与营气

Wei Qi is described as circulating at the surface, between skin and muscle, resisting external influences. Ying Qi is described as moving with the Blood and nourishing internally. They are two functions of one model, not two substances.

The nearest modern analogue people reach for is immune surveillance, but the mapping is loose and should be treated as a metaphor rather than an equivalence.