Following this, the Rivers Pollution Commission[8] of 1868 went on record as authority for the statement that "the existence of specific poison capable of producing cholera and typhoid fever is attested by evidence so abundant and strong as to be practically irresistible. These poisons are contained in the discharges from the bowels of persons suffering from these diseases." So it was that close observation and rigid inquiry discovered the truths that discharges from bowels of persons suffering from intestinal diseases contain the specific poison of the disease; that these discharges, mixed with the sewage of cities, often found their way into water supplies, and thus caused an epidemic of the same disease, and that boiling of water before drinking would destroy the infection, thus rendering it harmless. These truths stand to-day and the same means of prevention are resorted to in time of danger that were recommended during the epidemic of cholera in London in 1866. We know now, however, thanks to the investigations of Louis M. Pasteur, that all that class of disease which he designated as zymotic, are caused by little microscopic vegetation which gain lodgment in the body where they grow, multiply and thrive at the expense of the host; and knowing the specific cause of a disease makes it more easy to fight to prevent and to cure. [Illustration] [Illustration: THE·FOVNTAIN·OF·ELISHA· ·NEAR·JERICHO,·PALESTINE· From Stereograph, copyright 1899 by Underwood & Underwood, N. Y. (See page iv)] [Illustration: CHAPTER IX] SYNOPSIS OF CHAPTER. Introduction of Water Filters—Striking Example of their Efficiency and Value—Cholera at Altona and Hamburg—Purification of Sewage—The Automatic Scavenger of Mouras—Investigations of the Massachusetts State Board of Health—Garbage Destruction. As the suburban population around London, England, grew and occupied the drainage area from which the London water supply was obtained, just in such proportion was the water supply polluted, and London was early forced to devise measures for purifying an already polluted water; so it is that as early as 1839 London was filtering part of the water derived from surface sources, and so successful were the early attempts that at the present time although London is supplied with water by eight separate water companies, all of the water used within its confines which is derived from rivers, lakes or streams, is filtered before delivery into the distributing mains. Europe was not slow to grasp the value of filtration, and at the present time most cities of importance in Continental Europe have slow sand filters, while America, or at least the United States, which is reputed to adopt almost immediately anything which possesses merit, had constructed no filters as late as 1880, and to-day can number but few. A striking illustration of the value of filtration for sterilizing an infected water supply can be instanced in the cholera epidemic of Hamburg, Germany.