It will be appreciated that I cannot therefore consider the organism without its environment, and that from a formal point of view the two may be regarded as equivalent phases between which dynamic contact is maintained by the membranes that separate and link them.
(Mitchell P 1957. The origin of life and the formation and organising functions of natural membranes. In Proceedings of the First International Symposium on the Origin of Life on the Earth (ed. Oparin AI, et al. ), pp. 229–234 Academy of Sciences, Moscow)