Lack of swelling and shrinking of Pityrosporum ovale in media of different osmotic pressures and its relationship with survival in the relatively dry conditions of the scalp.

Pityrosporum ovale did not show the normal swelling and shrinking such as is undergone by Saccharomyces cerevisiae in media of different osmotic pressures. Pityrosporum ovale shrank slightly in media below 0.33 osmolar and remained at constant volume between 0.33 and 3-4 osmolar, while S. cerevisiae swelled below 0-10 osmolar and shrank markedly and progressively from 0.33 to 3-4 osmolar. The resistance of P. ovale to this effect is believed to be associated with its survival on the scalp in an environment low in water and high in salt from sweat, and to be a property of the remarkable construction of its cell wall as revealed by electron microscopy.