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What does the number on a fingertip oxygen monitor really mean?

A pulse oximeter uses light to estimate blood oxygen saturation. Its tidy display can conceal measurement limits, including effects associated with circulation and skin pigmentation, so one reading is not a complete assessment of a person's health.

4–5 min

Questions you could explore

  • How is an estimate different from a direct blood measurement?
  • What information does the display leave out?

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Health and the body

Daylight and the body's clock

Even in a room with no clocks, your body follows an internal roughly 24-hour schedule of sleepiness, hunger, and alertness. Those internal daily rhythms respond to outside cues, with morning and evening light helping reset and coordinate the body's master clock.

3–5 min

Daylight and the body's clock

Health and the body3–5 minEven in a room with no clocks, your body follows an internal roughly 24-hour schedule of sleepiness, hunger, and alertness. Those internal daily rhythms respond to outside cues, with morning and evening light helping reset and coordinate the body's master clock.

Health and the body

How vaccines build immune memory

The first time the immune system encounters an unfamiliar antigen, building a response takes time. Vaccines help develop recognition and memory before a later encounter with a pathogen. Different types introduce antigens or instructions for making them in different ways, offering a starting point for exploring how immune memory works.

4–5 min

How vaccines build immune memory

Health and the body4–5 minThe first time the immune system encounters an unfamiliar antigen, building a response takes time. Vaccines help develop recognition and memory before a later encounter with a pathogen. Different types introduce antigens or instructions for making them in different ways, offering a starting point for exploring how immune memory works.

Health and the body

Antibiotics and the viruses they cannot treat

Antibiotics can treat certain bacterial infections, but they do not treat the viruses that cause a common cold. Because bacteria are living cells with their own metabolic machinery and viruses are tiny genetic packages that hijack your cells, an antibiotic that disables bacteria has no matching target in the viruses that cause a cold.

2–3 min

Antibiotics and the viruses they cannot treat

Health and the body2–3 minAntibiotics can treat certain bacterial infections, but they do not treat the viruses that cause a common cold. Because bacteria are living cells with their own metabolic machinery and viruses are tiny genetic packages that hijack your cells, an antibiotic that disables bacteria has no matching target in the viruses that cause a cold.

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