21.   Hardheaded psi researchers know too well how easily magical-seeming experiences can have mundane explanations.

22.   Humans have a version of this gene, but the researchers do not know whether it affects the behavior of mothers.

23.   If estrogen did increase the risk of ovarian cancer, researchers do not know how.

24.   If the animals survive, researchers know the vaccine worked.

25.   It will be long before researchers will know whether estrogen can be tried as a stroke treatment for humans, however.

26.   Meanwhile, researchers in Eastern Europe knew galantamine could stimulate nerve cells to release acetylcholine.

27.   Medical researchers have long known that high lead levels can cause hyperactivity, reduced IQ and impaired growth in children.

28.   Moreover, researchers know that activity can keep neurons from atrophying.

29.   Muscle-building, researchers now know, is possible at any age.

30.   Now researchers know for certain that those earlier cases were bellwethers of a rapidly increasing phenomenon.