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.

On the river Elbe, some miles from the sea, there are three cities adjoining and forming in appearance one large city of 800,000 inhabitants, the combined sewage of which is discharged into the river Elbe. The water supply to the city of Hamburg, a free German city, with a population of 640,400, is derived from the Elbe above where the sewage is discharged into the river but not sufficiently far away to escape contamination from a recision of polluted water at flood tide. This water after some imperfect sedimentation passes direct to the consumer without filtration. The supply of water to Wandsbeck, a city of 20,000 population, is obtained from a lake which is unexposed to contamination and is filtered before being delivered to the mains. The supply to Altona, on the other hand, a Prussian city of 143,000 inhabitants, is obtained from the river Elbe at a point about 8 miles below where it receives the combined sewage of the three cities, with their population of over 800,000. It will thus be seen that the source of supply to Altona is the worst of the three. This most grossly polluted supply, however, is filtered with exceeding care before delivery to the consumers, and to this fact is attributed the freedom from cholera that visited Hamburg in 1892. The story is well told by Dr. Thorne, medical officer of the London Local Government Board.[9]

"The different behavior of Hamburg and Altona as regards cholera is extremely interesting. The two towns adjoin; they are practically one city. The division between the two is no more obvious than that between two densely peopled London parishes, and yet a spot map indicating the houses which were attacked with cholera, which was shown to me by Professor Koch, points out clearly that whereas the disease prevailed in epidemic form on the Hamburg side of the boundary line, that line running in and out among the streets and houses and at times passing diagonally through the houses themselves, formed the limit beyond which the epidemic, as such, did not extend. The dots on one side of the dividing line were proof of the epidemicity of cholera in Hamburg, their comparative absence on the Altona side of it was proof of the absence of the epidemic in Altona. To use Professor Koch's own words: 'Cholera in Hamburg went right up to the boundary of Altona and then stopped. In one street, which for a long way forms the boundary, there was cholera on the Hamburg side, whereas on the Altona side was free from it, and yet there was one detectable difference, and one only, between the two adjacent areas—they had different water services.' Professor Koch has collected certain proofs which he regards as crucial on this point, and Dr. Reincke has supplied me with a small plan in support of the contention. At one point close to and on the Hamburg side of the boundary line between Hamburg and Altona, is a large yard, known as the Hamburger-Platz. It contains two rows of large and lofty dwellings, containing 72 separate tenements and some 400 people, belonging almost wholly to those classes who suffered most from cholera elsewhere in Hamburg. But while cholera is shown by the spot map to have prevailed all around, not a single case occurred among the many residents of this court during the whole epidemic. And why? Professor Koch explains that owing to local difficulties, water from the Hamburg mains could not easily be obtained for the dwellings in question, and hence a supply had been laid in from one of the Altona mains in an adjacent street. This was the only part of Hamburg which received Altona water, and I am informed that it was the only spot in Hamburg in which was aggregated a population of the class in question, which escaped the cholera. At the date of my visit to Hamburg, a notice board was affixed at the entrance to this court. It stated that certain tenements were to let; but, above all, in large type, and as an inducement to intending tenants, was the announcement that the court was not only within the jurisdiction of Hamburg, with the privileges still attaching to the old Hanseatic cities, but that it had a supply of Altona water.

During the epidemic the deaths in the several cities were:

That infectious matter was communicated to the Elbe water from Hamburg is not in any way a hypothesis. Cholera germs had been as a fact found in the Elbe water. They were found a little below the place where the Hamburg main sewer flows into the Elbe. They were also found in one of the two Altona basins into which the water flowed before filtration."

No more striking example could be found, demonstrating on a large scale the efficiency of filtration as a preventive of water-borne diseases than that of the cholera epidemic of Hamburg in 1892, yet, at the present writing, there are people holding public offices throughout the United States who do not believe in the value of filtration as a public prophylactic, or who are so indifferent as not to advocate its adoption. Nor is this disbelief confined to public officials; many there are outside of public office who have made no study of sanitation and cannot believe that merely passing water downward through sand will purify it, and for the benefit of those who wish to be better informed, the story of the Hamburg epidemic of cholera, together with the part played by filters in saving Altona from a worse visitation, cannot be too often told.

It is but natural that, suspicion having once fallen on water as a source or vehicle of disease, means would be adopted not only to properly sterilize water before delivering it to the public, but, furthermore, to select the source of supply where there was least danger of contamination from filth. By this time public water supplies had progressed to such a stage that but few towns, cities or villages of any importance were without a municipal plant. Further, most cities of any importance had a more or less complete system of sewers, and the filth from these sewers was discharging freely, and in the crude state, into the streams and rivers of the realm. Such a condition of affairs could not last long without causing a nuisance, as well as becoming a menace to the health of the commonwealth, and it was not long before the problem was discussed of purifying the sewage before discharging it into streams and rivers. In Great Britain, the pollution of streams was felt more keenly than in America. The population along the rivers in Great Britain is quite dense, and the rivers, which are comparatively small, are used as sources of supply for the different municipalities along the banks, so that some means had to be devised to prevent the people up stream from polluting and perhaps infecting it for those lower down. So early as 1840, this matter forced itself on the attention of Parliament, and in 1843, a royal commission, the Health of Towns Commission, was appointed to inquire into the present state of large towns and populous districts. This was followed in 1857 by the Sewage of Towns Commission, a royal commission appointed to inquire into the best means of distributing the sewage of towns, and in 1865 by the Rivers Pollution Commission, a royal commission appointed to inquire into the best means of preventing the pollution of rivers.

Progress was not at a standstill during this time, however, but, on the contrary, chemical precipitation of sewage and purification by the application to land were striving with each other for supremacy. Up to that time, the important part that bacteria play in the reduction of organic matter was not understood, and instead of affording every advantage for the decomposition and fermentation of organic matter under the least objectionable conditions, the principal efforts of those interested in the problem were to prevent or put off as long as possible the septic action of sewage. It was not until so late as the year 1880 that attention was turned toward the possibility of the micro-organisms in sewage. In that year Dr. Mueller took out a patent endeavoring to utilize the micro-organism in sewage for the purpose of purification. According to Dr. Mueller's views, "The contents of sewage are chiefly of organic origin, and in consequence of this an active process of decomposition takes place in sewage through which the organic matters are dissolved into mineral matters, or, in short, are mineralized, and thus become fit to serve as food for plants. To the superficial observer, however, it is chiefly a process of digestion, in which the various, mostly microscopically small, animal and vegetable organisms utilize the organically fixed power for their life purpose.

"The decomposition of sewage in its various stages is characterized by the appearance of enormous numbers of spirilla, then of vibrios (swarming spores) and, finally, of moulds. At this stage commences the reformation of organic substance with the appearance of chlorophyl-holding protococcus."

About the same time, December, 1881, the account of Mouras's automatic scavenger was published in France. Mouras had been working and experimenting along the same lines as Dr. Mueller, and the result was an apparatus consisting of a closed vessel or vault, with a water seal which rapidly changed excrementatious matter into a homogeneous fluid, only slightly turbid, and holding the solid matters in suspension in the form of scarcely visible filaments. The principle claimed for his automatic scavenger by Mouras was that animal dejecta within themselves contained all the principles of fermentation necessary to liquefy them.

The teachings of Dr. Mueller and Mouras went unheeded for a long time, on account of the chemical processes then in vogue. It was maintained by those who were supposed to know, that lime and other antiseptic substances were particularly valuable in sewage purification, because they destroyed living organisms, such as bacteria, which give rise to putrefaction and fermentation. They contended that if all the organisms could be destroyed, that sewage would be rendered unobjectionable. So conditions stood when in January, 1887, Mr. Dibden read a paper before the Institute of Civil Engineers, in which he pointed out that the very essence of sewage purification was not the destruction of bacterial life, but the resolution of organic matter into other combinations by the agency of the micro-organisms. He pointed out, further, that a septic and not an antiseptic action was what was wanted, consequently any process which arrested the activity of the bacteria was the reverse of what was desired. Dibden's paper had the effect of turning investigation in the right direction, but a world of experimenting on a practical scale would be necessary before the practice of sewage purification could be established on a safe, sound and scientific footing. It remained for the Massachusetts State Board of Health to conduct those investigations, and so thoroughly was it accomplished that the records of their experiments furnish the basis for sewage purification practice in the United States. The experiments have been carried on since 1887, and the thoroughness and value of these investigations can be judged by the fact that during one period of twenty-two months four thousand chemical examinations were made in addition to the microscopic examinations.

Following the historic investigations of the Massachusetts State Board of Health, numerous engineers and investigators commenced applying to practice the principles there laid down, and with such good results that there are upwards of 200 purification plants in the United States to-day, and in Pennsylvania alone plans are under way at the present time for over one hundred sewage disposal works. Such a showing is encouraging, and leads to the hope that within a decade no city of any importance within the States will be pouring impurified sewage into public streams or lakes.

Up to within the last quarter century no thought was given in the United States to the disposal or destruction of the grosser particles which make up the waste of a large city, nor was provision made at sanatoria, hospitals and like institutions for the destruction of materials which might prove infectious; yet, no less important than the removal of sewage by water carriage is the systematic collection and subsequent destruction of all matter of no value which might prove a vehicle of disease, if a clean, sanitary environment is to be maintained. The necessity for such removal and destruction was first felt in hospitals, sanatoria, barracks and camps, where many people are brought together under unusual circumstances, and infective matter is liable to accumulate, thereby proving a menace to the community. It is not surprising, therefore, that the desirability of destroying such accumulated wastes was first brought home to the medical staff connected with military service, and that the medical authorities should be connected with the British army.

The first garbage destructor, or garbage furnace, of which there is any record, was constructed about 1860, at Gibraltar, for the exclusive destruction by fire of all waste matter from the British garrison. In the United States, likewise, it was at the army posts where the need for waste destructors was first felt, and in 1885 Lieutenant H. I. Reilly, U. S. A., built the first American garbage furnace at Governor's Island, New York Harbor. From that time on, the value of garbage destructors became more widely known, and within recent years the need for a sanitary and convenient method for disposing of waste matters has been occupying the attention of those in charge of institutions devoted to the care of the sick, infirm, feeble, and to the control of the criminal. In addition to the superintendents of hospitals, prisons, sanatoria and asylums, those in charge of medical schools and laboratories, hotels, business houses and municipalities have given the matter much consideration, and at the present time most of the large cities of the United States have constructed garbage destructors, or are seriously considering the step, while the principal hospitals, hotels, department stores, medical colleges and public institutions throughout the country have already installed destructors. Likewise, garbage destructors have been constructed at all of the United States Government army posts.