In the episode "The Paradise Syndrome", Dr. McCoy says to Spock:

Dr. McCoy: [scanning Spock] Well, your Vulcan metabolism is so low it can hardly be measured, and as for the pressure, that green ice-water you call blood...

Mr. Spock: My physical condition is not important, Doctor. That obelisk is.

Star Trek: The Original Series, "The Paradise Syndrome"

Why does McCoy say this? It was my understanding that Vulcans are warm-blooded.

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    It may be that McCoy was speaking in relative terms. Meaning that Vulcan physiology is such that body temperature and blood pressure norms (i.e. thinner blood) are both noticeably lower than a human's. The fan-made (and not generally accepted as canon) "Star Fleet Medical Reference Manual" explicitly states both. But again, that work is not widely considered canon, so it's still just speculation on my part.
    – Helbent IV
    Jul 7, 2018 at 5:24
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    "warm-blooded" doesn't mean your blood is higher in temperature than a cold-blooded animal, it just means that your body actively expends energy to maintain a constant body temperature (about 98 degrees F for humans). So-called "cold-blooded" animals adjust their body temperature to match their surroundings. So in a frozen tundra the human will be 98 degrees (on the inside) and a lizard will be frozen through, but in a scorching desert the human will still be 98 degrees and the lizard may be hotter. Jul 7, 2018 at 9:39

1 Answer 1


McCoy and Spock have a traditional feud; McCoy thinks that Spock is too logical and "cold-blooded", making decisions without emotion (and Spock of course thinks the reverse). So he is once again making a dig at his long-time rival in the guise of a medical report, and Spock is telling him to knock it off and focus on the job in front of them.

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    This answer would benefit from noting that someone who remains calm in the face of danger is said to have ice water in their veins. Jul 7, 2018 at 5:15
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    @DavidConrad Somehow, I completely forgot that expression, possibly because it's a little more complimentary than I would expect from Dr. McCoy.
    – Cadence
    Jul 7, 2018 at 5:31
  • McCoy has referred to Spock's blood in other episodes, that it is based on copper I think comes up. Their feud also can get pretty serious as in the case of Spock and McCoy marooned in some ice age cave with Marriette Hartley.
    – Jeff
    Jul 7, 2018 at 6:17
  • Can you support this answer with evidence? Not evidence that McCoy and Spock have a feud -- that is well established -- but that McCoy teases Spock with statements that are contradictory to fact.
    – DrSheldon
    Jul 7, 2018 at 15:51
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    @DrSheldon Not as such, unfortunately, but I can say definitively that no canon source in over 50 years has said anything about Vulcan blood literally running cold, despite plenty of opportunities. (We're told about their metabolism, neural structure, digestion, reproduction, even their teeth, and plenty about blood chemistry, but nothing about it being cold.) McCoy's poetic usage fits with his role as the "humanist" on the command staff and his general character; otherwise we have to conclude that either McCoy is mistaken or the writers were.
    – Cadence
    Jul 7, 2018 at 19:18

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