This book reconstructs the emergence of the phenomenon of “lost time,” i.e. the interval between stimulus and response, with respect to the German physiologist Hermann von Helmholtz (1821-1894) and the French writer Marcel Proust (1871-1922). It argues that the discovery and explanation of this phenomenon was closely tied to the functioning of laboratory technologies. In the winter of 1849/50, Helmholtz conducted pioneering measurements concerning the propagation speed of stimulations in the living nerve in Königsberg by using electromagnetic devices and graphical instruments. When presenting his findings in the Parisian Academy of Science, he coined the term “lost time” in order to illustrate the delays accompanying the functioning of nerves. In the 1910s, Proust adopted the same expression from the popular writings of the French physiologist Etienne-Jules Marey.