Science: How Eggs Grow

At the University of Tennessee’s Oak Ridge experiment station, hens fed with mildly radioactive mash are laying radioactive eggs. This tracer technique, the university said last week, has helped its poultry scientists to follow the intimate workings of the hen’s egg-making machinery. By skilled use of Geiger counters, they can follow the “hot” feed as it circulates inside the hen. They can measure it accurately as it forms into an egg.

A new-laid egg, say the scientists, contains material derived from feed that the hen ate as long as 40 days before. It takes eight to ten days to form a complete egg. Most of this time (about seven days) is spent in the making of the yolk. The shell is a quickly built container. Nearly 75% of the mineral in it comes from feed that the hen ate the previous day.