Experiments are described in which it is shown that the estrogenic hormone (α-estradiol propionate) increases the amount of extracellular fluid in the skin. Since previous work showed that this hormone increases resistance of rabbits to vaccinia virus, it is suggested that the increased resistance is the result of increased fluid in the tissues.
In further test of this thesis, experiments were performed in which the extracellular fluid in the skin was increased by the intraperitoneal injection of a salt solution known to increase the hydration of the tissues. Under these conditions it was found that the spread of India ink in the skin, as well as susceptibility to viral infection, was decreased in the same magnitude as obtains when the animals are treated with estrogenic hormone. The identity of effects under the two sets of circumstances seems to warrant the conclusion that in both instances the spread of India ink and decreased susceptibility to vaccinia are due to the common factor of increased volume of the extracellular fluid.