The age of scientific realism associated with Harvey's discovery of the circulation of blood and Vesalius' description of the structure of the body sired a small number of chemists and physiologists. Among these, Jean Baptiste van Helmont made contributions in both scientific areas. He described carbon dioxide, studied the growth of plants, recognized the acidity of gastric juice and its importance in the first stage of digestion, and examined quantitatively the urine of patients with nephritis. His writings, several published after his death, reveal an underlying mysticism, but, struggling with the unknown in chemistry and biology, he found them susceptible to scientific study and measurement. Thus, he typifies the transition from alchemy to chemistry.
Jean Baptiste was born in Brussels of a good family; he studied at the University of Louvain trying first one faculty, then another, and eventually deciding that his love was medicine. Having initially spurned an academic