In this essay, I sketch a problem-based framework within which I locate the concept of "organism" in the system theories of Georg Ernst Stahl, Théophile Bordeu, and Paul-Joseph Barthez. Around 1700, Stahl coins the word "organism" for a certain concept of order. For him, the concept explains the form of order of living bodies that is categorically different from the order of other (dead) bodies or composites. At the end of the century, the "organism" as a specific form of order becomes a major topos in many discourses. I will not so much focus on experiments and objects as on basic problems that contribute to the general framework of the concept of organism as a key concept of the vitalist movement between 1700 and 1800. For this purpose, I will investigate the combination of three explanatory tools. These tools refer to regulating agents, functional interactions, and stimulus-reactions-schemes within individual organic systems of forces. They are related to various themes--especially to energy, sensibility, and sympathy. I will retrace some aspects of these relations.