51.   Doctors know little about how it is spread.

52.   Doctors know that.

53.   Dr. Gary Larsen, the head of pediatric pulmonary medicine at the University of Colorado School of Medicine, said that doctors have not known how to assess wheezing.

54.   Doctors do not know what causes a heart attack to occur suddenly when it takes years for the underlying damage to develop.

55.   Doctors have known for decades that a high dose of birth-control pills taken shortly after sex could prevent pregnancy.

56.   Doctors have known for years that the methotrexate-misoprostol combination can be used to induce abortions.

57.   Doctors have known of cases like this for years, without understanding them.

58.   Doctors have long known that patients do not religiously comply with most medication regimes.

59.   Doctors have long known that the infection, acute otitis media, can be treated without antibiotics.

60.   Doctors have long known the difficulty of determining what prompts certain outbreaks of disease, despite the best medical sleuthing by forensic pathologists and epidemiologists.