The Structure of the Yolk of the Hen’s Egg, Investigated by Means of Its Permeability to ⁸²Br

⁸²Br was mixed with the white of hen’s eggs maintained at I° C., and its concentration in the yolk and white measured after experimental periods ranging from 5 min. to 200 hr. In some cases the distribution of ⁸²Br in the yolk was determined.

From 5 hr. onwards the concentration in the yolk increased at a constant rate reaching on the average 2-5 % of that in the white after 200 hr. This suggested that the penetration was opposed by an external membrane of low permeability (7 × 10⁻⁵ cm./hr.).

Before 5 hr. the amount of ⁸²Br in the yolk was in excess of that predicted by this mechanism. This did not appear to result from contamination from the white and suggested that there was a layer of yolk external to the resistive external membrane and therefore this was not the vitelline membrane.

Even after 100-200 hr. most of the ⁸²Br which had penetrated remained in the superficial layers of the yolk. This showed that there was also a resistance to its penetration in the mass of the yolk itself.

The bearing of this evidence on the structure of the yolk is discussed.