In the work ‘Life Itself’, Rosen showed that a formal mechanism cannot be ‘closed to efficient cause’. Additionally, he claimed that organisms are ‘closed to efficient cause’ and that, by logical extension, organisms cannot be mechanisms. This paper shows that it is possible for mechanisms to be ‘nearly closed to efficient cause’, with the requirement that some unentailed efficient-cause agents are placed inside the system. Populations of these ‘nearly closed to efficient cause’ systems can be defined based on the ability to isolate each component in its own ‘reaction chamber’. Diagrams from these populations are drawn from a couple of different perspectives, and comments are made on how these diagrams can be related to the more conventional language of chemistry.