“cells seemed to he enveloped by a selectively permeable layer that allowed different substances to enter and leave cells at significantly different rates. He recognized that lipid-soluble substances penetrated readily into cells, whereas water-soluble substances did not. He concluded that lipids were present on the cell surface as some sort of a "coat." Irving Langmuir (1881-1957) proposed that that cells were covered by a lipid monolayer.”
