Louis Pasteur, the scientific giant who gave us pasteurization and the vaccine for rabies, said this about making scientific observations: "Chance favors only the prepared mind."

Alexander Fleming had such a prepared mind. Upon returning from a two-week vacation in 1928, he noticed that he had left out a culture plate smeared with staphylococcus bacteria in his laboratory.

As a result, it had grown fungus.

Before tossing it away, however, he observed that the fungus had stopped the bacteria from growing. This observation turned his forgetfulness into felicity, for Fleming's prepared mind saw the fungus as more than fungus.

He saw it as a way to stop bacteria from thriving in the body.

From Fleming's error evolved penicillin, now one of the most prescribed drugs in the world because of its effectiveness in thwarting ear infections; heart infections; inflammation in the lungs, kidneys, liver, muscles, and bones; and pneumonia.

Something similar with sleep, I feel, has happened recently. Researchers who began experiments to learn more about it are now discovering the inexorable link between a sufficient amount of it and optimal health.

Consider, for instance, work done with 27 healthy middle-aged subjects by researchers from St. Luke's-Roosevelt Hospital and Columbia University and published in the American Journal of Physiology. Subjects were studied during a six-day period where they slept for either nine hours or four hours a night.

They were given six weeks to normalize and were then observed again, this time sleeping for the other amount of time.

Both times subjects were fed meals matching their energy needs to maintain their current weight for the first four days of observation. At meals during the final two days, subjects were instructed to eat as much as they wished.

From this, a pattern emerged. After sleeping fours hours a night, subjects reported a perceived increase in hunger and ate more calories, carbohydrates, and fat than after nine.

In a study published in the October issue of Sleep, a lack of sleep in teenagers was correlated to an increased production in insulin, creating insulin resistance and an increased risk in type 2 diabetes.

Researchers tabulated sleep duration for 245 high school students for one week. By interpreting this information, they found that if those who normally sleep six hours a night get seven, their insulin resistance would improve by 9 percent.

Of special significance is that the average for all participants during the week was only 6.4 hours but the school-night sleep average was "significantly lower."

Yet sleep seems to affect more than just body weight. A study from Canada and published in Pediatrics connected sleep with school behavior.

Working with healthy seven- to 11-year olds, the Canadian researchers found subjects who slept one hour less than their normal were more likely to be emotionally unstable, restless, and impulsive the next day in school. Similarly, they found that increasing sleep time by 27 minutes on the nights before school days led to more emotional stability, less restlessness, and less impulsivity.

As a result of this work, the researchers wrote that "healthy sleep is essential . . . for academic success. Sleep must be prioritized, and sleep problems must be eliminated."

While links between weight gain and poor behavior have been previously linked to insufficient sleep, new work first reported at this year's American Academy of Pediatrics National Conference and Exhibition has linked a lack of sleep in teens with an increase in sports injuries.

From questionnaires filled out by a total of 112 junior high and high school athletes in Studio City, California that asked respondents how much total time they spent playing their sport, how much weight lifting they do, what their typical sleep patterns were, and a number of other related items, researchers were able to determine that the more sleep the athletes got, the less likely they were to sustain an injury.

No other factor such as how many hours they practiced, if and how often they lifted weights, how many total sports they played, if they had a private coach, if they found sports "fun" could be linked to an increased rate of injury.

Somewhat like the discovery of penicillin, the link between sleep and teenage sports injuries occurred by accident. Senior author of the study, Matthew Milewski, M.D. said: "When we started this study, we thought the amount of sports played, year-round play, and increased specialization ins sports would be much more important for injury risk."