The Relations Between Yolk and White in the Hen’s Egg

Abstract

1. The freezing-points of white and yolk in the hen's egg gradually approach equality when the egg is kept for long periods; and the rate of the process of equilibration is rapid at first but becomes very slow as equality is more closely approached. 2. Between 0° and 25° C. the rate of equilibration has a temperature coefficient (Q 10) of from 1.5 to 2. At 25° C. equality of freezing-points is reached after about 70 days. 3. Equilibration is achieved partly by the passage of water across the vitelline membrane from white to yolk, but partly also by more complicated changes of osmotic concentration occurring more or less independently in white and yolk. 4. The recovery of hypertony by a yolk, previously diluted by immersion in water, when it is replaced in egg-white can, be explained on the basis of a temporary heterogeneity of the diluted yolk, and this explanation is supported by experimental evidence. 5. The rate of equilibration is much greater when the separated yolk is placed in mixed egg-white than in the intact egg, but since it is also greater in thin white than in thick white, and greater again in the white dialysate, the structure and viscosity of the white are probably important factors. 6. There is evidence of an appreciable resistance to water-movement both in egg-white and in egg-yolk. 7. In hypotonic or hypertonic aqueous solutions of glucose or glycerol, or in Ringer's solution, the rate of equilibration is greater than in egg-white and many times greater than in the intact egg. Water is taken up by the yolk both from hypotonic and hypertonic solutions of Ringer, within the range δ = 0.10° to 1.20° C., at a rate which increases the further the solution is removed from the point of isotony. 8. Evidence that the apparent disequilibrium in intact eggs is not a steady state maintained by a "Lebenswirkung," is afforded by: (i) the form of the equilibration curves, which strongly suggest the slow attainment of an equilibrium by diffusion, rather than a steady state terminated by death; (ii) the temperature relations of equilibration, which are consistent with the former assumption, but which do not agree at all with the effect of temperature on the viability of fertile eggs; (iii) the absence of any tendency of the yolk to maintain its hypertony when the white is concentrated by rapid evaporation; (iv) the alternative explanation for the recovery of hypertony by diluted yolks, which was the most crucial evidence for the existence of a steady state maintained by the expenditure of energy.