PHILADELPHIA – One afternoon in mid-July, Melissa Morris-Ivone was on the receiving end of one of those infinitesimally small acts of kindness that put you in a good mood.

She was waiting for the elevator in a Philadelphia office building. The doors opened. She turned to the middle-aged guy next to her and gestured for him to enter first.

“But he did the gentlemanly thing,” she says. He insisted she have the honor.

How nice, right? Polite. Considerate. “It caught me off-guard,” she says. For the rest of the day, she felt terrific. “I started thinking, why don’t we all do that more often?”

Shortly thereafter, Morris-Ivone, a 28-year-old graphic designer, started OperationNice.com – a blog for her campaign to share stories of kindness. The idea, she explains, is that good will is contagious. The more you think about it, the more you spread it around. Now, two months later, she has reached a few hundred people around the world and stumbled into a growing let’s-be-sweet cybertrend.

Evidence the self-explanatory ifoundyourcamera.net, started by a student in Winnipeg, Manitoba, and the SpreadLoveProject.com, and thinkbuddha.org, which welcomes good karmic input. Actsofkindness.org receives about 15 posts each week chronicling – what else? – tales about people being nice.

The proliferation of blogs and Web sites dedicated to goodness is still modest, but notable, given the stupefying misanthropy on the Internet.

“I do think it’s a big trend,” says Alyssa Wright, who launched heroreports.org in June. Wright, 30, was working on her master’s degree at the Center for Future Civic Media at the Massachusetts Institute of Technology when she dreamed up the Web site where New Yorkers could post anecdotes about acts of generosity or thoughtfulness.

“These sites may be in response to a certain amount of sadness about the way Americans are positioned in the world. The cruelty we’ve been a part of,” Wright says. “It’s a backlash, I think. We need the balance. So these sites focus on our sense of humanity and compassion.”

Newspapers and TV report major acts of heroism, passers-by rescuing babies from burning buildings and such. Wright’s site captures less-dramatic moments. Like the immigrant who was offered a couch to sleep on until he could find an apartment. And the woman who stepped up to her ankle in a paint puddle and was offered a turpentine cleanup by an artist who lived nearby.

Wright’s personal examples include the subway engineer who stopped his off-duty train to give her and a friend a ride on a freezing winter night. And the Brooklyn coffee shop full of strangers who got down on their hands and knees to help her find the diamond that had fallen out of her engagement ring.

“It’s not surprising that there’s so much out there about people being nice,” says Zeynep Tufekci, an assistant professor of sociology at the University of Maryland who studies the social impacts of technology.

“We’re influenced by the idea that people are selfish. It’s really not true.” While humans do compete for survival, she says, they also cooperate. “We like to be liked. And we admire people who help others. It’s a very fundamental human characteristic.”

The Internet, she adds, amplifies the good feeling you get from giving and receiving acts of kindness.

“It makes a lot of sense,” says Martin Nowak, a professor of mathematics and biology at Harvard. Nowak develops mathematical models to understand why people are nice to one another.

The research inspired the concept of upstream reciprocity. “It’s the idea that when someone was just nice to you, you feel elevated, so the next person you meet, you’ll be nice to them.”

Without knowing about the scientific evidence, Morris-Ivone sensed the dynamic.

She’s naturally the kind of person who gives people the benefit of the doubt, even when they’re cutting her off on the Betsy Ross Bridge: “I always think, maybe they didn’t know they were doing it.”

She’s the kind of person who, at the supermarket, donates a dollar for leukemia research. And at red lights, drops change into the buckets of kids raising money for basketball camp.

“I thought there should be something to encourage people to be nice. It’s such a harried society. Maybe we need a reminder.”

Morris-Ivone, who lives in Cinnaminson, N.J., started searching for heart-warming stories. She googled “home town hero” and combed through newspaper archives. “It was difficult finding anything uplifting,” she said.

A few days later, she started the blog and invited her friends to share anecdotes about how they’d been treated thoughtfully in any way, big or small.

Small, it turns out, makes up the majority.

Kind acts tend to be spontaneous and sporadic, says William Hamrick. The milk of human kindness, in other words, is more splash than flow.

“Most people do just want to be nice,” says Hamrick, a retired philosophy professor and author of “Kindness and the Good Society.” “But they tend to act randomly” – seizing on opportunities when the spirit moves them. “So, as a basic philosophy that frames their lives, they may not always hold to the highest ethical standards, but they’ll run after you when you leave your glasses in a restaurant.”

Morris-Ivone had no idea how effective her efforts would be. But she was willing to produce 100 postcards with simple suggestions, “Hold the Door,” “Offer to Help,” “Smile,” and to send them (at her own expense) to anyone who asked.

Within a few weeks, she’d had 80 hits on the blog, including some from visitors around the world. One in France and another in Spain offered to translate her postcard for distribution in Europe.

There is an inherent paradox, she has to admit: using the Internet, which can be such a faceless, anonymous meeting place, to encourage greater face-to-face interaction. The alchemy seems to work nonetheless.

“Good Samaritan behavior is often hard to document,” notes Denise Anthony, associate professor of sociology at Dartmouth College. “It’s usually a one-time thing, a stranger helping someone anonymously. What’s new is that online forums, blogs and listservs provide a way of sharing that information, and magnifying the attention to the good instead of the negative.”

Geography, race and economics, it turns out, have nothing to do with kindness. Wright is collecting data from her site to create a Hero Map.

“I think it has the power to change how we view our communities,” she says.

Furthermore, the kindness Web sites break down the presumption that small-town folks are more soft-hearted than those who live in cities.

There is no such correlation, Hamrick says. “The environment doesn’t make the person.”

And reading about goodness can have a positive influence only on those who are inclined to be influenced.

“Grinches and scrooges,” he says, “need much more incentive than just reading a blog.”