Abstract
An examination of a sample of the eggs obtained over a year from four birds, each of four breeds, namely, White Leghorn, Black Leghorn, Rhode Island Red and Light Sussex, has been made. This examination included studies of percentage of cracked eggs, shell thickness and porosity, membrane thickness, total shell nitrogen and insoluble and soluble fractions. All these characteristics varied widely from bird to bird, but, despite this, all except porosity showed marked breed differences too, although on the basis of quantitative values, no one breed excelled in all characteristics. Shell thickness declined in the summer months and membrane thickness was very low in April, but no other characteristic appeared to be affected by the season. Shell thickness of itself was not a guide to the cracking of eggs but for any one bird the cracked eggs had the thinner shells. There was also a possibility that the cracked eggs had the thicker membranes. Thin‐shelled eggs had a higher nitrogen content and this has been explained on the basis of shell structure. The close relationship between weight of true shell per unit area and shell thickness has been reaffirmed and it is suggested that weight per unit area is an easier, more reliable and quicker method of obtaining relative thicknesses of shells, than is the measurement of shell thickness using a micrometer screw gauge.