ID a sci-fi story?

A short story or novella, I read it in the early 1970s, probably written in the 1950s or 1960s, and probably end in an anthology. A scientist has some fast growing small (microscopic?) organism in the lab. It reproduces a lot and quickly, so he can watch generations of evolution in a matter of days. The organisms evolve intelligence, civilizations, and…and…that’s all I got. Help, anyone?

Microcosmic God” by Theodore Sturgeon

That’s it! Many thanks!

I’ve created Lutherans!

Have you looked in your fridge lately?