Porosity of, and bacterial invasion through, the shell of the hen's egg

Abstract

1. Histological methods show four layers in the intact shell of the hen's egg, namely, cuticle, spongy layer, mammillary layer, and inner shell membrane. Distinct channels or pores may be found in the spongy layer, but these tend to disappear in the mammillary layer in which only a network of much finer channels can be observed.2. Viscometric measurements of the passage of water and air through the shell show that(a) shells vary widely in their porosity, even when taken on successive days from the same hen;(b) there is no correlation between porosity so determined and the number of pores counted by staining methods;(c) the rate of flow is slower from the interior to the exterior than vice versa, and the pore count by staining methods also less on the inside than on the outside.3. A rough correlation exists between porosity as determined viscometri-cally and the evaporation of water during storage.4. If the temperature of the egg is higher than a fluid containing bacteria in which it is immersed, the latter are readily drawn through the shell by simple suction as the egg cools down, a point of great significance in the washing of eggs.