Impacts of laboratory methodology on medical thinking in the 19th century

During the 19th century the first laboratories at hospitals and clinics in Central Europe were established. These 'clinical laboratories' were devoted to chemical analyses in practical medicine and clinical research. A characteristic feature of these laboratories was the use of measuring instruments, e.g. volumetric apparatus, polarimeters, spectroscopes, colorimeters, photometers. Using these techniques new phenomena were introduced into clinical medicine which could serve as signs in the diagnosis of diseases. Many of the new diagnostic signs were quantitative data as results of measurements. Their main advantage was the greater differentiation in the description of phenomena compared with the qualitative data used before. Another important characteristic of the new diagnostic signs was the discovery of causal relations to physiological and pathological processes in the organism. The physicians and chemists in the clinical laboratory were eager not only to collect empirical data but also to find causal relationships by research work similar to that carried out in physics and chemistry. Once causal chains were been identified more general relationships became clear. One example is the concept of metabolism which comprised a dynamic view on chemical processes in the body and the variation of "Stoff" (material) in time, including a quantitative input-output analysis of the body in health and disease. In the second half of the 19th century, scientifically based diagnostic signs began to replace the traditional symptoms and signs used since antiquity.