The investigation of gastric digestion was now pursued by a versatile Italian, the abbe Lazaro Spallanzani (1729-99), who showed that the churning action is an aid, but not an essential to the process of digestion (1782). He proved that digestion was not of the nature of putrefaction and differed essentially from the fermentation of wine. Spallanzani thus improved on the view of Sylvius and took a step towards that solution of the natures of putrefaction, fermentation, and digestion which was finally pro vided by Pasteur. He showed that the gastric juice was secreted by the stomach itself, and not introduced into it from other organs. He observed that it curdled milk and so began our knowl edge of a separate ferment, that contained in rennet. Spallan zani's results showed that gastric juice had a solvent power sui generis, and that this was of a different order from putrefaction or vinous fermentation.
This phase of digestive physiology was closed by the English physician, William Prout (1785-1850), who demonstrated in 1823 the existence of free hydrochloric acid in the stomach. He showed that the presence of this acid was necessary for gastric digestion, but that the actual process of solution of food was the work of another agent. The matter was at last brought into the range of medical practice by an American army surgeon, William Beaumont (1785-1853) who, in the ten years ending 1833, had the opportunity to investigate gastric juice in a man who, having been shot in the stomach, had a permanent gastric fistula, through which the gastric juice could be obtained and the living gastric membrane examined at will.
of Bologna, while investigating the susceptibility of nerves to irritation, showed that nervous action could be induced by elec trical phenomena (1791). He was, as a matter of fact, producing an electrical current. Many thought at the time that a new kind of electricity of specially animal origin had been produced and they called it "galvanism." Alessandro Volta (1745-1827) of Pavia, deviser of the "Voltaic pile" was able to demonstrate (1800) that galvanism is without any essential animal relation ship and that a muscle can be thrown into continuous contraction by repeating electric stimulations. Humbug and misunderstand ing in connection with the electrical relations of living tissues were rife, and it was not till after the period we are now considering that electricity came to take a place in rational medicine. The change came with E. du Bois Reymond (1818-96) from onwards.
During the second half of the i8th century, important advances were made in the knowledge of respiration on the basis of the work of the Scottish chemist, Joseph Black (1728-99). Black was aware that chalk, when heated, is transformed into quicklime, thereby losing its power of effervescing with acids but gaining the power of absorbing water. As expressed to-day the changes are : The first achievement of Black was to show that in the process of heating to quicklime the chalk lost weight. This was a blow at the phlogiston theory, for it had been supposed that quicklime consisted of chalk plus phlogiston. Black now showed that if slaked lime be treated with a mild alkali, such as carbonate of sodium, it changes back to the state in which it was before heating, in fact into chalk, while the mild alkali is converted into a caustic alkali. As we now express it : Black's triumph consisted essentially in showing that reactions (I) and (3) were indefinitely reversible and that the same amount of could always be extracted from (3) as was put into ( 1). The substance given off by the chalk in (I) and ab sorbed by it in (3) he named "fixed air." We now call it carbon dioxide. The conversion of caustic lime into ordinary chalk by exposure, proved this "fixed air" to be a normal constituent of the atmosphere.