These source materials appeared between 1940 and 1960 CE.
The Mystery of Sex by Charles Waldemar (1958)
The Perfect Matrimony: Why Sex and Religion are Inseparable by Samael Aun Weor (1950)
Sex Perfection and Marital Happiness by Rudolf von Urban, MD (1949)
Thinking and Destiny: Being the Science of Man by Harold Waldwin Percival (1946)