parative psychology, analogous to comparative anatomy, which latter has been in an advanced stage for a long time. Finally, in the psychological domain we owe to modern times the knowledge of the strange phenomena of double consciousness and of hypnotism with the phenomena of suggestion, the study of which is calculated to throw on the mental being more light than could the most voluminous works on psychology of former times, which were the result of self-observation and self-deification. Unfortunately, these phenomena have given food to the inextirpable belief in miracles, and furnished new support for unfounded spiritualistic and spiritistic chimeras of every kind, such as thought-reading, telepathy, magnetic rapport, the belief in ghosts, spooks, etc.
Medicine.—If we finally mention medicine or therapeutics as a branch of physical science we have here also to record a series of the most important advances in the course of the century. At the head stands the method of auscultation or of listening by means of an ear trumpet to the sounds in the chest in order to discover disease in the lungs and the heart. This method was invented by the French physician Laennec in 1819, soon after the method of percussion had been improved by Piorry, while the foundation of pathological anatomy through Professor Rokitansky, and of pathological histology by Professor Virchow, which soon after followed, advanced medicine to a real science. Another invention, highly important in practice—subcutaneous injection—was made by A. Wood in 1850. More recent than all this is the very important discovery of the infectious micro-organisms or bacteria as the causes of disease. This discovery, which led to the application of disinfection, in common with the introduction of chloroform and cocaine as anæsthetics, on the one hand, cleared the way for the acknowledged wonderful progress made in surgery, and, on the other hand, materially facilitated the combating of diseases caused by those organisms by prophylactic measures.
We must also allude to the invention of a great number of new remedies obtained by means of chemistry, as well as of new methods of curing ailments (e. g., massage). We must mention, too, the general introduction of vaccination, which has proved one of the greatest blessings to mankind. Whether the injection of fluids as an immunity against certain diseases (e. g., diphtheria), tried according to the same method, will fulfill the hope entertained is a question the solution of which must be awaited after the unfortunate failure of a similar procedure employed in tuberculosis. It seems, however, as though this so-called "serum therapeutics" in its further development might accomplish great results in the field of infectious diseases. The ascertaining and location of internal diseases (particu-
