One-fifth of a teaspoon

I was brought up short by this odd sentence in a NY Times article on attempts to protect health-care workers treating Ebola patients:

At the peak of illness, an Ebola patient can have 10 billion viral particles in one-fifth of a teaspoon of blood. That compares with 50,000 to 100,000 particles in an untreated H.I.V. patient, and five million to 20 million in someone with untreated hepatitis C.

“One-fifth of a teaspoon” is an odd reference unit. I had to think a moment to realise that the reporter had presumably translated into American from Scientific the sentence

At the peak of illness, an Ebola patient can have 10 billion viral particles in one milliliter of blood.

As I discussed before, the partial conversion to the metric system has left fault lines between and within nations. And the attempt to cover over those cracks mechanically creates odd dissonances. Thus, the 19th century estimate of average human body temperature of 37 degrees Celsius (plus or minus about half a degree) gets turned into the incredibly precise sounding 98.6 degrees Fahrenheit. It makes as much sense as saying “28 grams of prevention are worth 454 grams of cure”.

If the reporter had thought about it, she might have translated less mechanically, writing “an Ebola patient can have 50 billion viral particles in a teaspoon of blood”. But that still leaves the weird resonance of “teaspoon of blood”. A millilitre can be water or blood or Martian atmosphere, but when I hear “teaspoon” I subliminally feel like it’s supposed to go in my tea, or cake, or soup. The thing that people like so much about these traditional units is their historical and narrative specificity, their attachment to human-scale measuring activities, but that also makes them awkward for transferring measurements between domains. I could state my height in furlongs, and my weight in grains, but I’ll just confuse people.

Before posting, I just wanted to check that I was right about the size of a teaspoon in milliliters. I asked Google, and received the information “1 Imperial teaspoon =5.91939047 millilitres”. So, first of all, I was surprised to learn — if indeed it is true — that the teaspoon has been standardised to the hundred-billionth of a litre. Second, I found the thought of “the imperial teaspoon” hilarious.

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