This dissertation elucidates the cybernetic response to the life question of post-World War II biology through an analysis of the writings and experiments of Warren S. McCulloch. The work of McCulloch, who was both a clinician and neurophysiologist, gave rise to what this dissertation refers to as a biological, medical cybernetics, influenced by vitalist conceptions of the organism as well as technical conceptions of the organ, the brain. This dissertation argues that the question ‘what is biological life?’ served as an organizing principle for the electrical, digital model of the brain submitted in “Of Digital Computers Called Brains” (1949) and the formal, mathematical model of the brain required by the McCulloch-Pitts neuron in “A Logical Calculus of the Ideas Immanent in Nervous Activity” (1943). I argue that, in discussions in these papers of how the brain responds to stimuli, there is a concept of biological life as perceptual life, rendering the brain a biological object with technical attributes whose activity is the activity of world-building. This dissertation analyzes experiments McCulloch performed on living animals to understand how the cybernetic brain was pharmacological and not merely digital or automatic. Finally, this dissertation analyzes writings on the discipline of biology published late in McCulloch’s life, which concern the information carrying capacity of water molecules, the reproductive protein called the “Biological Computer,” and a thought experiment on building a simulation of man. I claim that McCulloch’s “Biological Computer” includes a model of heredity counter to that of DNA, where form and not the program bears life forward.