An introduction to, and some new, anatomical and physiological aspects of the cervix and vagina are presented, and also an explanation of the biosynthesis and molecular structure of mucus.

The history of my discoveries of the different types of cervical mucus is given. In considering my microbiological investigations I suspected the existence of different types of crypts and cervical mucus and in 1959 I proved the existence of these different types.

The method of examining viscosity by nuclear magnetic resonance was applied to microsamples of mucus extracted outside of several crypts. Preliminary studies in 1966 proved the existence of two types and in 1977 the three types G, L, and S mucus were described. Sperm cells were transported in S mucus, L mucus attracted malformed sperm and G mucus formed a plug in the cervical canal in the infertile phases.

In 1990 a new mucus, P mucus, was characterized. A mucolytic enzyme, probably emanating from the isthmus of the cervix, was associated with this mucus and facilitated the upward movement of sperm cells. At the end of 1993 another mucus, F mucus, was identified. This mucus is probably produced by foetal
cells remaining in the wall of the neck of the uterus.

Variations in these different types of mucus throughout life and during the course of a cycle, and their importance for the Billings Ovulation Method®, are presented and discussed.