The Impact of Determinism in the Life Sciences of the 19th and 20th Centuries
At the end of the 18th century, the progress made in studying the chemistry of gases and the clarification of the idea of the chemical reaction brought an end to a first stage in the application of the experimental method to the understanding of living beings. The theory of the four elements, earth, air, water and fire, which had been inherited from the philosophers of Ancient Greece, was replaced by a rational classification of known chemical species. At the beginning of the 19th century, the English chemist John Dalton introduced the idea of atoms being the elementary components of chemical species. This atomic theory signaled the start of a series of progressive steps made in the chemical sciences. Physiology was waiting for this progress to be made in chemistry, in order to be able to evaluate, or even to quantify, metabolic modifications that are inherent to vital processes such as digestion, respiration, muscular contraction or nerve impulses.