I called to explain it to you.
You see I've been investigating the causes of epidemic diseases.

Some scientists think they are spread by molecules in the air; others attribute them to gases generated in the sewers; others hold that they are conveyed by contagion; but I--" "Aid you goig to tague thad idferdal thig away frob here ?" asked the major.
"But I have discovered that these diseases are spread by the agency of door-mats.

Do you understand?
Door-mats! And I'll explain to you how it's done.

Here's a man who's been in a house where there's disease.
He gets it on his boots.

The leather is porous, and it becomes saturated.