Some mysterious gravitational force seems to group my mail by subject before I open it. So it was no surprise that envelopes 13 and 14 in last Monday's stack of donations to Children's Hospital were both from mothers. The subject of both: sons.

"Today is my 87th birthday," said the letter inside Envelope 13, "and I decided to send a check for that amount, as an additional 'thank you' for the wonderful care Children's Hospital gave my son, Jack, when he was 6 years old and suffering with double pneumonia.

"He just called to wish me a Happy Birthday -- my six feet, six inch 53-year-old son, who is now a professor at Georgia Institute of Technology.

"I told him I was going to send the check and he said, 'Mother, that is fine.'"

Envelope 14 was a shocker. It contained a $10 check and a letter. The signatures on both were very, very familiar.

"Dearest Bob," the letter said. "I wonder if more mothers than anyone else give to the Children's Hospital? What about your mother?

"I find myself reading your daily column and remembering the (happily) rare times you and I used hospitals when you were young. Mostly I remember that dreaded phone call one Saturday when you had gone to play football and they phoned and said you had a 'slight' concussion and to come and get you. We proceeded to the emergency ward where I was supposed to keep you awake. What a trauma!

"Please accept my check for Children's Hospital. I can't think of a better cause for this money. It buys so little by itself, but added to all your other contributors, it helps to keep a worthwhile institution going."

Thanks, Ma. I may have been dumb enough to mash myself into semiconsciousness as a high school football player. But that doesn't mean I can't appreciate a good cause when I see one. Obviously, I inherited that ability from someone-or-other.