This paper focuses on the early interpretations of the concept of gas, originally created by J. B. Van Helmont (1579 <FONT FACE=Symbol>¾</FONT> 1644). Our main interest is on the ideas of English physicians and chemical philosophers of the seventeenth century. Gas was usually associated with the material cause of diseases, with the vital spirit, or with a volatile spirit produced in some kinds of material transformations. As a general trend, however, the authors who did not want to embrace the details of the medico-chemical system proposed by Van Helmont preferred to use more well-known words (such as vapours, exhalations, effluvia, odours, spirits), avoiding the use of the neologism.
gas; seventeenth-century chemistry; plague
