X-Message-Number: 15085
Date: Wed, 06 Dec 2000 22:33:11 +0000
From: Philip Rhoades <>
Subject: Petri dish antics

>Message #15082
>Date: Wed, 06 Dec 2000 16:25:32 +1100
>From: Damien Broderick <>
>Subject: Petri dish antics
>Forgive this quibbly question. Bill Walker sez:

Actually it was me (Phil)  . .

> >If you have a bacterium that
> >doubles in number every day in a petri dish and it takes 10 days to
> >completely cover the dish - then on the last day, the petri dish is still
> >only 50% covered!
>It's always been a nice image, but is it true?

More or less . . I could've used grasshoppers on a wheat field or something 
but you get the picture . . Malthus was right (with a few minor reprieves 
due to modern technology).  A human population growing at a few percent a 
year, doubles in about 20 years.

>I've never grown bugs on
>glass or plastic, but intuition tells me they can only readily spread from
>the circumference of their territory (unless they send spores jumping out
>through the third dimension).

Depending on the bugs they do both . .

>Once they've eaten their substrate, don't the
>guys inside the perimeter have some trouble replicating?

That's true, depending on the bugs and the growth media you will get die 
off in the middle . .  but that doesn't hurt the analogy much . .



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