He endorsed the view of elements as the undecomposable constituents of material bodies; and made the distinction between mixtures and compounds. He made considerable progress in the technique of detecting their ingredients, a process which he designated by the term "analysis". He further supposed that the elements were ultimately composed of particles of various sorts and sizes, into which, however, they were not to be resolved in any known way. He studied the chemistry of combustion and of respiration, and conducted experiments in physiology, where, however, he was hampered by the "tenderness of his nature" which kept him from anatomical dissections, especially vivisections, though he knew them to be "most instructing".