What staining technique outlines structures that are not taken up by their target tissue?

Negative staining is a technique specifically designed to highlight structures that do not absorb the stain effectively. This method is particularly useful for visualizing delicate or transparent specimens, such as certain cellular components. Instead of staining the cells or structures themselves, negative staining creates a contrast by staining the background, allowing the unstained structures to appear against this colored backdrop.

This technique is essential in microscopy because it provides a clear perspective of shapes, sizes, and arrangements of cells or organelles without the complications that can arise from overstaining.

In contrast, other techniques mentioned, like counterstaining, is used to provide a contrasting color to specific structures after they have already been stained, making those structures more discernible. Direct staining typically involves applying a stain directly to the tissue to visualize the structures that retain the dye. Supravital staining is a technique that is applied to living cells and is beneficial for observing cell behavior in a living state but does not serve the purpose of highlighting unstained structures.