You are studying an animal and inject fluorescein, a fluorescent dye, into a single cell on the surface epithelium of the animal. After a brief period of time, the dye spreads to cells neighboring the injected cell. What do you conclude

The cells are connected by gap junctions.

Explanation:

A gathering of protein channels, which permits small molecules and ions to move between the neighboring cells is termed as a gap junction. The protein channels that form gap junctions comprise two connexons, of which one is situated in the membrane of one cell that combines and aligns with the connexon of the adjacent cell.  

This association produces a spontaneous pathway, which permits the small molecules and ions to pass passively from one cell to another. The gap junctions are found in all the kinds of cells, however, they are not found in skeletal muscle, RBCs, and blood lymphocytes.  

Thus, the passing of the fluorescent dye from one cell to another shows that the two cells are connected with the help of gap junctions.