3. BACTERIAL EXAMINATION.
When sanitarians generally came to recognize that the constituents that impart a dangerous character to polluted water were living organisms belonging to the class of bacteria, it seemed to many a fair inference that by testing for the presence of these bacteria more accurate and direct information could be obtained as to the safety of a water than by testing for chemical substances which were not in themselves injurious. Projects for the bacterial examination of water were consequently entered on with much enthusiasm, but the original expectations excited by this mode of procedure have by no means been realized. It was soon found that the search for specific pathogenic bacteria in water was but rarely crowned with success, and that among the multitude of bacteria present in sewage and polluted water but few could be regarded as dangerous; it is now manifest that for the present the