Note 21 — Chapter VII · STRUCTURE AND GROWTH OF SKIN.

Under the microscope, the skin is of course lighted from above by direct light from a window, or by that of a lamp concentrated by a “bullseye” condenser. The reversal of the image in the microscope often causes a pseudoscopic effect very puzzling to the beginner, prominences appearing as hollows, and vice versa till the real direction of the lighting is considered.