Abstract: The surface of a cellular body which is flat except for a number of cavities is examined by placing a transparent light refracting medium against the surface and transmitting light through the medium toward its interface with the body surface at such an angle of incidence to the interface that light incident on the interface at the body surface is refracted into the body and light incident on the interface at the cavities is totally reflected internally of the medium and then outwardly thereof. The reflected light produces an image having readily distinguishable zones of lightness and darkness indicative of the cavities and body material, respectively. The image is displayed in such manner as to enable either of the relatively dark and light zones to be counted. An optical coupling liquid is interposed between the body surface and the refracting medium to compensate for small gaps or irregularities in the body surface.