Justus von Liebig, of Giessen, was and long remained the dictator of the chemical view of life. He did more than any other man to introduce laboratory teaching into medicine. The many scientific advances that he initiated are considered under his name, but we may note, first, his method for detecting and measuring urea, a substance regularly formed in the course of the bodily processes; secondly, his introduction, along with his colleague \Wailer (1800-82), of the conception of the "radicle" as a chem ical group capable of forming an unchanging constituent through a series of compounds; thirdly, his doctrine that animal heat is the result of combustion and is not "innate"; and fourthly, his teaching that plants derive their carbon and nitrogen from the carbon dioxide and ammonia in the atmosphere, and that these compounds are returned to the atmosphere by the plants in the process of putrefaction, thus producing a sort of circulation in nature.
Claude Bernard, the greatest physiological experimenter that has ever lived, did more than any other physiologist to create the view of the body as a machine in which all the parts are inter dependent. In the course of his researches on the action of the liver, he showed that the body could build up very complex chemical substances as well as break them down. He did pioneer work in elucidating the digestive functions, and in explaining the regulation of the blood supply.
Karl Ludwig, who had more pupils than any other of the great physiologists, published most of his work in their names. He was very ingenious as a deviser of physical apparatus, and was very well equipped in physics and chemistry. He was responsible for introducing graphic methods into science in general, and into physiology in particular. In doing this he was particularly f or tunate in adapting the device of the kymograph, which had been originally introduced by Thomas Young in 1807. Ludwig applied himself to every branch of physiology. He was a mechan ist and he is important in this connection because of his success in showing that glandular activity can be brought under the law of conservation of energy.
In connection with this process of integration comes the impor tant question of the localization of the functions of the brain. This idea was developed in the first third of the 19th century by the Viennese workers, Franz Joseph Gall (1757-1828) and Johan Caspar Spurzheim (1776-1832) who ultimately developed into phrenological quacks. Later a number of observers—Paul Broca (1824-8o) (q.v.), Hughlings Jackson (1834-1911) (q.v.) and David Ferrier (1843-1928) (q.v.) among them—studied the parts of the cortex- specially connected with movement. Many opera tions previously regarded as involving complex mental processes, such as speech, reading, writing, drawing, etc., have been repre sented as depending on simple nervous relationships. Centres for the initiation of these operations have been described. Of late there has been reaction from this mechanical conception of the brain as an organ of the mind, especially under the leadership of Sir Henry Head (b. 1861). The older school has, however, achieved striking clinical successes, especially at the hands of Jean Marie Charcot (1825-93) (q.v.) and his school. (See BRAIN: