Brown said two of his crewmen recently found themselves bickering on a job at the Riviera.

"It was over nothing," he said. "And one of the guys quit and never came back."

Heat is a form of stress.

"Anytime we're under extreme stress, our ability to handle it gets challenged," said Las Vegas psychologist David P. Gosse.

Kevin Oliver, fire management officer for the Bureau of Land Management, cited 110 degrees as "the breaking point for our fighters."

"You're not really in good shape mentally if you haven't been conditioned in the heat," he said.

In 1986, a novel experiment linking temper to temperature was conducted by Douglas Kenrick and Steven McFarlane of the University of Arizona psychology department. They drove up to red lights in Phoenix, refusing to accelerate when they turned green. They measured the frequency and length of honks they received from drivers behind them during different parts of the year.

"Below 80 degrees, people would politely tap the horn after a few seconds," Kenrick said. "When it got above 80, people leaned on the horn longer. And that continued to go up such that, when it was above 100 degrees, people leaned on the horn the majority of the time."

Heat is so uncomfortable because the body is consistently striving to keep its core temperature at 98.6 degrees.

"When body temperature gets above 105, the proteins of the body start to malfunction and break down," said Dr. William Harrington, emergency-room physician at Southern Hills Hospital. "They have a very sensitive temperature range in which they can function normally. When they stop doing that, then the body has a great deal of difficulty running its normal metabolism and the entire cell mechanism breaks down."

The cells that are most sensitive to temperature, Harrington explained, are brain cells. So emotional symptoms often manifest themselves before physical ones.

"In heat injuries that are severe enough, the nervous system starts to malfunction and people get confused or actually pass into coma," Harrington said.

Crime statistics seem to bear the temper/temperature correlation out. Southern cities, on the average, have higher murder rates than northern ones. In addition, two studies published in 1997 found violent crime increasing in step with thermometer mercury in various U.S. cities from 1950 to 1995.

Harrington, who worked at University Medical Center from 1993 to 2006, said he consistently saw "a significant increase in both gunshot wounds and knifings" during the summer months. He estimated that increase at 10 percent to 20 percent.

However, heat is a difficult factor to isolate. Harrington, who has since shifted to Southern Hills Hospital, said the increase he saw "may also be because more people are housebound because of the heat." In addition, he said, "alcohol may play into that as well."

Officer Bill Cassell, Metropolitan Police Department spokesman, said that his department records crimes, but not the temperature outside when they occur unless it's relevant to the case.

"But I can tell you that anything that increases the stress on a community, sometimes causes an increase in the criminal activity," he said. "Sometimes when people become uncomfortable, they become less tolerant of other individuals, which can lead to criminal activity."