 While Rheinberger’s account of experimental research in biology is right to put its emphasis on experimental systems rather than on theories, it may be criticized for the ontology of experimental systems that it contains. On this account, experimental systems are construed as very inclusive entities. They contain not only the specific materials and apparatus necessary to do research, but also the preparatory procedures, lab protocols, storage devices, measurement techniques, and so on. Thus, it is clear that such systems are not only composed of material entities; at least some of the constituents of experimental systems are conceptual in nature. For example, a lab protocol that describes how to prepare a cell extract that will be able to carry out protein synthesis in vitro is really a conceptual entity. A researcher who is following such a protocol is not merely manipulating materials, lab equipment or symbols. Rather, she is acting under the guidance of concepts. (Action is always behavior guided by concepts). Among these concepts there may be what used to be known as “observation concepts” such as “supernatant”, “pellet”, “band”, and so on. Furthermore, the protocol will contain terms such “microsomal fraction”, which is supposed to designate a certain sediment produced by centrifugation that contains microsomes (vesicles of endoplasmic reticulum membrane). Thus, the protocol also contains theoretical terms.