RACHEL CADE (320 pp.)Charles MercerPutnam ($3.95).
This is the story of an American missionary nurse's love affair with Africa. Slim, thirtyish Rachel Cade can take sex or leave it alone, but she is not really interested in it. She quits her first post because a married doctor keeps breathing amorously on her neck. At her next post, Dibela, in the Belgian Congo, the resident doctor dies the night she arrives, leaving her the only white within miles. In short order she climbs the sacred Mountains of the Moon and invites a couple of thahus (curses) from the local medicine men. So there...