Scientists generally record their laboratory activities and experimental results in notebooks, from which they construct scientific papers. The Johns Hopkins physiologist William Henry Howell kept a laboratory notebook from 1913 to 1914, in which he recorded experiments on the blood clotting factor prothrombin. In 1914 he published a paper using this notebook, to justify his theory of prothrombin activation. Howell's paper is reconstructed, in terms of its narrative and argument elements, from the laboratory activities and experimental results recorded in the notebook. This reconstruction reveals an intimate connection between the two texts and the process by which Howell constructed a scientific paper. The generation of scientific knowledge by Howell is then evaluated, especially in terms of theory formation and justification.