Surgical mask and refrigerator: what they have in common

1. Step 1. Surgical mask — uses — Germ theory of disease. Protection against droplets.
2. Step 2. Germ theory of disease — is used in — Vaccine. Pasteur developed vaccination on the basis of germ theory.
3. Step 3. Vaccine — uses — Cold chain. Cold storage.
4. Step 4. Cold chain — uses — Refrigerator. Refrigerators.

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