Mycobacterium vaccae

There is nothing that makes me feel better than walking in the grass barefooted.
Or digging with bare hands or laying and looking at the sky.
I always believed that the reason was simply being close to nature, but today I read the reason could be something else:
"Mycobacterium vaccae is a natural soil bacterium which people likely ingest or breathe in when they spend time in nature," says Dorothy Matthews of The Sage Colleges in Troy, New York, who conducted the research with her colleague Susan Jenks.

Previous research studies on M. vaccae showed that heat-killed bacteria injected into mice stimulated growth of some neurons in the brain that resulted in increased levels of serotonin and decreased anxiety... "This research suggests that M. vaccae may play a role in anxiety and learning in mammals," says Matthews. "It is interesting to speculate that creating learning environments in schools that include time in the outdoors where M. vaccae is present may decrease anxiety and improve the ability to learn new tasks."