How We Found Out Germs Exist

Step 1 of 5

The two wards had wildly different death rates.

A Vienna hospital in the 1840s admitted mothers to two wards on alternating days. One was staffed by doctors and students, the other by midwives. Women begged to be sent to the midwives' ward, and they were right to.

Step 2 of 5

Every obvious explanation was tested and failed.

Overcrowding: the wards were equally full. Climate: both were in the same building. The priest's bell, thought to frighten the patients, was rerouted — no change. The women's birthing position was changed to match — no change.

Step 3 of 5

Then a colleague died of the same thing.

A friend of Semmelweis cut his finger during an autopsy and died with exactly the symptoms the mothers had. That was the connection: the doctors did autopsies each morning and went straight to the delivery ward. The midwives never touched a corpse.

Step 4 of 5

So he made everyone wash in chlorine.

Not for hygiene — soap and water was already normal. He chose chlorinated lime because it removed the smell, and he reasoned that whatever caused the smell was the thing being carried. The death rate in the doctors' ward fell to match the midwives' within a month.

Step 5 of 5

He was right, and it was rejected anyway.

He could not explain why it worked — germ theory did not exist yet — and the claim implied that doctors had been killing their patients. He was dismissed, and the practice lapsed. Pasteur and Lister supplied the explanation twenty years later.

What a germ actually is — and why bacteria and viruses are not the same thing — is its own page.