How did Justus von Liebig study metabolism from a chemical viewpoint?

Justus von Liebig pioneered the study of metabolism from a chemical perspective in his 1842 work, Animal Chemistry or Organic Chemistry in Its Applications to Physiology and Pathology, which is regarded as a foundational text of modern biochemistry.1

To investigate metabolic processes, Liebig utilized chemical analyses and highly speculative equations. His goal was to map the pathways through which foodstuffs are transformed into flesh and blood, as well as the processes by which tissues are degraded to produce animal heat, muscular work, and various secretions and excretions.1

Although many of the specific details in his metabolic schemes were later proven incorrect, his novel methodological approach of applying chemical principles to living processes proved highly influential. By challenging his hypotheses, subsequent researchers were able to uncover many important scientific principles. For example, while his chemical theories regarding fermentation and putrefaction were inaccurate, they encouraged physicians to adopt a chemical theory of disease, which helped shift medical understanding away from the prevailing belief that disease was caused by miasma.1