Electroencephalograph and vacuum pump: what they have in common

1. Step 1. Electroencephalograph — is made of — Silver. The electrodes are silver with silver chloride.
2. Step 2. Silver — is material for — Syringe. Early needles were silver.
3. Step 3. Syringe — works like — Piston pump. A syringe is a hand-operated piston pump.
4. Step 4. Piston pump — evolved into — Vacuum pump. Guericke adapted the piston pump to pump out air.

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