"Jan Baptist van Helmont (bapt. January 12, 1580 – December 30, 1644) was an early modern period Flemish chemist, physiologist, and physician. He worked during the years just after Paracelsus and iatrochemistry, and is sometimes considered to be "the founder of pneumatic chemistry". Van Helmont is remembered today largely for his ideas on spontaneous generation, his 5-year tree experiment, and his introduction of the word "gas" into the vocabulary of scientists."
http://en.wikipedia.org/wiki/Jan_Baptist_van_Helmont