There are some questions in biology that you’d think were settled long ago. For instance: How many types of cells are there in the human body?

“If you just Google this, the number everyone uses is 200,” said Jay Shendure, a geneticist at the University of Washington. “But to me that seems absurdly low.” A number of scientists like him want to build a more complete catalog.

Yet there are an estimated 37 trillion cells in the human body. The traditional ways to identify cell types — such as carefully tracing the shape of individual cells under a microscope — are too slow and crude for the job.

On Thursday, Dr. Shendure and his colleagues published a report describing a speedy new method for taking such a cell census. Instead of inspecting one cell at a time, they measured the activity of genes inside 42,035 cells at once.