Following six months of failed attempts under intense observation by geriatric scientists, Briarwood Nursing Home residents Horace Klass, 86, and Helen Veukmaan, 83, successfully mated in captivity Monday. 'As with most new arrivals to Briarwood, Horace and Helen at first seemed despondent,' Briarwood's Dr. William Stander said. 'Before long, though, they grew accustomed to their new habitat, and Horace soon felt comfortable enough to approach Helen. Indeed, Horace ultimately proved quite aggressive.' Briarwood employees report that, after mating, Klass provided Veukmaan with half a box of windmill cookies. 