Israel. A father and his children. The Bible tells man to be fruitful and the Talmuc tells him when the woman is fertile. The mystery of conception has until recently been incased in myth. But what still remains a mystery is how the anicent Rabbis came to understand the prescribe laws regulating when a may be be with his wife, and when not. Science has now uncovered what the Rabbis knew, the fruitful period of a woman.