tests show that it has lost nearly all its power of pollution. Thus, the number of 198,000 bacteria per cubic centimetre found by Prausnitz at the mouth of the Munich sewer was reduced at Ismaning to 15,231, and at Freising to 3,602. A similar result was obtained by Frankel with the water of the Spree at and below Berlin. The mere number of bacteria found has, however, no sanitary significance, since these particular microbes are mostly harmless, and in fact destroy the pathogenic microbes in the struggle for existence. The purifying action of rivers is ascribed by von Pettenkofer to the oxygen dissolved in the water in a free state or separated from organisms. In the latter respect the green algae and even non-chlorophyllic plants come prominently into consideration. This vegetation should be preserved; but it may be destroyed by a too great concentration of the water to be purified; and to prevent this, industrial waste waters which destroy vegetation must be kept out till they have been purified.
Bacteriological Processes against Disease.—According to a summary in the Saturday Review, attempts by bacteriological processes to remove from the human system the germs of infectious disease have been made by six different methods. The first is by Pasteur's preventive inoculation, in which a minute quantity of an attenuated culture of the virus is administered to produce a light attack of the disease. The second is M. Pasteur's method in rabies, in which a mitigated virus is injected into a person already attacked with the disease, to overtake it. The third is the employment of the virus of a comparatively mild disease to protect against a more severe one, as in vaccination for smallpox. Next in order is the destruction of the disease-producing bacteria by the administration of antiseptics or bactericides. A fifth method is the re-enforcement of natural means possessed by our systems for combating disease germs: by re-enforcing the leucocytes or white blood-corpuscles, which destroy bacteria, by means of the injection of the blood of animals insusceptible to the disease; by raising or lowering the temperature of the body of the patient; by alterations of diet, climate, or surroundings; or by injection of phagocyte invigorators. The sixth method is by the injection of the "toxalbumens" formed by the bacteria growing in artificial cultures, as is done in Koch's method for tuberculosis. That these methods have not proved entirely satisfactory, and bacteriological treatment is now apparently at a standstill, is not due, it is thought, to any innate defect in the system, but to some technical detail. "When the ingenuity of man has arrived at the point of being able to prove absolutely that organisms, completely invisible to all but the highest magnifying powers attainable, cause each its particular infectious disease; when these tiny things may be made to grow like plants in a garden, separately and in order; when we can keep rows of tubes each with its deadly contents on our laboratory shelves, or in our incubators, like druggists' bottles of inert powders or crystals—surely we shall not stop at this stage in our control over this 'world of the infinitely little.'"
A clarification of muddy liquids and partial separation of micro-organisms is effected by M. R. Leze by subjecting the liquid to a rapid rotation. Thus, cider, in turbid fermentation, after being whirled in a turbine wheel, came out clear; and while specimens kept in bottles at 86° soon generated bacteria, the yeast and alcoholic fermentation had all disappeared. This method may be found useful in bacteriological investigation; and in industrial operations, for ridding impure and unhealthy waters of most of the organisms contained in them.
Chemical analysis has been applied by M. Berthelot to the solution of a problem in archæology. Taking a piece of copper found by M. de Sarzec in his explorations of the nuns in Mesopotamia, which was obtained from one of the most ancient sites, he made an exact determination of its composition. It contained no tin or zinc, and only slight traces of lead and arsenic. It had been oxidized throughout, and presented itself as a suboxide or a mixture protoxide and metallic copper. Hence, while the question can not yet be considered decided, the specimen is a contribution of evidence in favor of the existence of an age of copper.
The physicians of Massachusetts have in recent years noticed a development of malarial disease in Cambridge and the vicinity of Boston and in other towns of the State. The origin of the cases in Cambridge seems, from the investigations thus far made, to be