The story of Ignaz Semmelweis might be the greatest example of the law of unintended consequences in action.

Today, childbirth is a relatively routine process, with the current rate of maternal death in developed nations being a mere nine women out of 100,000.

But times weren't always so good. In the 1840s, childbirth was extremely risky, due to a condition now known as puerperal fever. Healthy women would arrive at the hospital, contract the raging fever, and die within days. This condition flummoxed even Europe's best hospitals at the time, including perhaps the finest hospital of the time, Vienna General Hospital.

The statistics at the time were terrifying. From 1841-1846, 20,000 babies were delivered at Vienna General, with nearly 2,000 of the mothers dying. The situation worsened in 1847, with 1 in every 6 women dying of puerperal fever.

Then a young man joined Vienna General. His name? - Ignaz Semmelweis. His name might not be familiar to you now, but he probably saved billions of lives with a quick, clever change to the system.

Semmelweis was deeply distraught at all the deaths from this strange disease, and conducted an investigation in the hospital. From his early research, he gathered that while different doctors provided a variety of explanations for the condition, from foul air in the delivery wards to the presence of male doctors, none of them really knew what was going on.

So Semmelweis turned from doctor to data detective. He was attempting to solve this troubling puzzle: When women delivered babies at home or with a midwife, they were sixty times less likely to contract puerperal fever than with a trained doctor or medical professional. After analyzing data from his own hospital, Vienna General, which had two separate wards for delivery, one staffed with midwives and female trainees, and another with male doctors, he found that average death rate in the doctors' ward was more than twice as high as that in the other ward.

Having discredited all the other ridiculous theories floating in the air, Semmelweis proceeded to establish some facts.

• Even the poorest women who delivered their babies and then came to the hospital did not contract the disease.
• Women who were dilated for 24 hours almost certainly contracted the disease, as opposed to those who were dilated for a shorter time.
• The disease could not have been contagious, because the doctors did not catch it from the mother or the newborn.

But as much credit should go to Semmelweis for his remarkable analysis, his realization came by accident. An older professor and a friend of Semmelweis suddenly died by a freak accident. As he was leading a student through an autopsy, the student's knife slipped and cut the professor on the finger.

The professor suffered a series of grave maladies before dying, which Semmelweis noted, were almost identical to those inflicted on mothers with puerperal fever. There was no ambiguity about the professor's cause of death. It was caused by "cadaverous particles introduced into his vascular system."

The cat was finally out of the box. In recent years, first-rate hospitals like Vienna General practiced autopsies as a method of studying anatomy. What better way to study illness than to sift through the diseased, malfunctioning organs in question? At Vienna General, every single deceased patient was taken to the autopsy room for examination.

But the doctors and medical students who came from the autopsy room went directly to the maternity ward with at best, a quick washing of their hands. The germs from the autopsy carried themselves all the way to the maternity ward, where the constant prodding and poking of the uterus by the doctors allowed them to fester and cause puerperal fever.

Semmelweis immediately ordered all doctors and medical students to disinfect their hands in a chlorinated wash after autopsies, to make sure that all germs were rid of. The rate of maternal death dropped to a whisper above one percent, saving millions, perhaps billions of lives in the process.

But where does the law of unintended consequences come into all of this? It's a piece of sheer irony that doctors, in the pursuit of medical knowledge that could save thousands of lives, conducted autopsy after autopsy, which, in turn, led to the loss of thousands of lives.

[1] SuperFreakonomics ( SuperFreakonomics: Chapter 4 ).

N.B. Some of the data is taken from the above source, but the text is original.