Fig. 4. Fluorescent photomicrographs showing the simultaneous imaging of redox state and reactive oxygen species in hydroid cells in vivo. Each pair of images is the same cross section of the epitheliomuscular cell fibers at the base of a living polyp shown at NAD(P)H (A,C) and fluorescein (B,D) wavelengths (each fiber is approximately 2µm in diameter): A,B, negative control, 24h after feeding, treated with DMSO but not H₂DCFDA; C,D, 24h after feeding, treated with H₂DCFDA (fibers are relatively reduced; H₂O₂ is abundant).