The Meaning Of Life – Part Twenty Eight Of Forty Two
July 31, 2014
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Do larger mammals take longer to urinate than smaller mammals?
When I was a young schoolboy, I well remember a teacher, when describing Roman religious practices, coming up with the killer line that he had never seen an auspice. How we all roared! Now that I am a mature adult I have seen a horse piss and a prodigious quantity of steaming urine they produce, to be sure. I have also had the privilege of watching many other species of the animal kingdom passing water. I don’t know if it is just serendipity or whether the sight of me causes them to micturate.
Anyway, I have long wondered whether it takes a creature the size of an elephant longer to urinate than a horse, for example. It is these sorts of questions, I find, that nag away at you and which this series is intended to answer.
Help is at hand from some research conducted at Zoo Atlanta in Georgia and published in the ever popular Proceedings of the National Academy of Science. The researchers, who assuming that because creatures like a rhino have bigger bladders than a dog, thought that the animals with larger bladders would take longer to go about their business and set out to prove this by installing high-speed cameras to capture their performance. Thirty two species ranging in size from a mouse to an elephant including jaguars and gorillas were tested.
The findings were fascinating. It wasn’t the size of the animal’s bladder that was the key determinant but their overall size. The tipping point for mammals is a weight of 6 lbs. Despite an elephant having a bladder capacity of 18 litres compared with a cat’s of 5 millilitres, all mammals with a weight in excess of 6 lbs urinated on average for 21 seconds, give or take.
It is all down to flow rates, apparently. An elephant can urinate faster than a cat because its urethra is wider and longer, allowing the force of gravity to act more strongly on fluid flowing through it. Creatures with weights below 6 lbs, on the other hand, have urinary tracts that are so small that they have to battle against capillary action – a tendency for the urine’s molecules to stick to themselves and the walls of their tracts and flow back up again. Instead of producing a stream of urine, their pee is so viscous and moves so slowly that it falls out in droplets.
Fascinating stuff and useful too. If you are unfortunate enough to be stuck in a shower of elephant urine, at least you now know that your ordeal will last around 21 seconds. Makes it seem almost bearable!
So now we know!