 Glisson had arrived at his position as a result of physiological research on the stomach and intestines, in which he noticed that these and other parts of the body were sensitive to touch even though there were no nerves present. This is the phenomenon now known as irritability, but in his efforts to explain it Glisson had developed a general theory of matter and body and had published it in his Treatise on the Energetic Nature of Substance (Tractatus de natura substantiae energetica, seu, de vita naturae, 1672).