An Improved Procedure for Counting Pores in Avian Eggshells

Abstract

Efforts to count pores in avian eggshells have most often made use of procedures first described by Tyler (1953). In general, eggshells are boiled in a solution of NaOH to remove shell membranes and free organic matter from pore mouths and pore channels, etched with acid (usually nitric acid) to enlarge the pore channels, and then treated with a dye (usually methylene blue but also other dyes as in Ar and Rahn 1985) to make pores visible and countable. Typically, the dyes are applied to the inner surface of a shell fragment in water solution. After application, capillary action moves the dye solution to the outside surface of the shell where its appearance in pore mouths makes counting of pores possible. A number of other procedures has been used to count pores in avian eggshells. Tyler and Fowler (1979) painted the outside surface of eggshells with acid fuchsin to highlight grooves and pore mouths. Hoyt et al. (1979) projected light through previously etched pore channels and then counted screen images. Tullet (1975) applied procedures of scanning electron microscopy (SEM) to the inner surfaces of eggshells. Silyn-Roberts (1983) used SEM techniques in conjunction with uranium-stained pores to specifically identify nonobstructed pore channels. In this note I describe still another procedure for counting pores. The procedure has the following attributes: (1) it is simple to apply; (2) it makes actual counting easy; (3) it provides some information about pore size.