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supply which has pharmacy viagra cheap become polluted. But in most cases the procurement of such an unpolluted supply is prac- tically barred by financial considerations. We are therefore reduced to one of two alternatives either to limit pharmacy viagra cheap as far as possible or to prevent absolutely (which is practically impossible) the access of im- purities to the sources of supply, or else to purifv the water after it has become polluted. It will be found to be practically impossible, in most instances, to abandon a source of water supply that may be pol- luted and go a great distance in search of a pure supply. The expense of such an undertaking is too great. Fortunately, however, we have a means at hand for purifying a polluted water supply. This is filtration. Formerly filtration meant simply straining out from water all gross impurities and changing a dirty or muddy water into a clear and pharmacy viagra cheap limpid fluid. We now know that water may be perfectly clear and pharmacy viagra cheap limpid, and yet be extremely impure by reason of its content of organic matter or dangerous micro-organ- isms. A great impetus to filtration was given by the experiments conducted under the auspices of the Mas- sachusetts State Board of Health at Lawrence in that State, and carried out so thoroughly by Mr. Hiram F. ;io MEDICAL RECORD. [May 1 6, 1S96 Mills and Mr. Allen Hazen. These experiments, carried chinese viagra online on with painstaking care for a number of years, prove conclusively that water, no matter how polluted, can be rendered pure by simply filtering the same through sand filters, provided certain cautjons are observed regarding the construction of the filters, the rate of nitration, and other conditions varying with the character of the water to be purifkd. For many years, filtration through sand has been used by European municipalities to secure purification of water, and the construction and practical management of filters have been investigated with great care. Comparative studies of the efficiency of sand filters and of various processes of so-called "mechanical filtration" have been made recently in Providence, R. I., chinese viagra online and at Lawrence, Mass. While the pharmacy viagra cheap results ob- tained by different investigators have not been in entire agreement, the prevailing opinion of sanitarians and engineers is that sand filtration, where it can be adopted, gives the best results in purification, at the lowest cost of construction and maintenance. Koch has given a clear explanation of the process of sand filtration. The real filtration, he says, does not take place in the sand, but, by deposit from the still un- purified water, a layer of mud is formed on the top f the sand, and this is the chinese viagra online real filter which retains the suspended constituents from the water. The im- portant points are that a proper layer of slime should be formed, that it should not be disturbed during the process of filtration, and that when by further continu- ous deposit it becomes too thick, and therefore too im- permeable to water, it should be removed. Different natural waters are capable of producing the filtering mud layer in very different degrees, according pharmacy viagra cheap to the amount of mineral and vegetable matter held in sus- pension. In sand filtration, therefore, we are not deal- ing chinese viagra online with so simple a matter as is often supposed. The sand layer should never be allowed to get below a cer- tain thickness, about thirty centimetres, and a speed of about one hundred millimetres in the hour must be allowed for the movement of the water chinese viagra online through the sand layer to obtain the most perfect purification. Koch further states that a daily or tri-weekly bacterio- logical examination of the filtered water must be made in order to test the performance of the filter. If a filter works satisfactorily in even - respect, experience shows that there will be found less than one hundred germs capable of development in one cubic centimetre of water, and this is irrespective of the number of bac- teria contained in the water before filtration. The slightest changes in the rapidity of filtration, or the disturbance of the surface of the filter bed, become manifest on bacteriological examination. The cholera epidemic in Hamburg in 1892 fur- nished an object lesson of great value. Hamburg and chinese viagra online Altona both draw their water supply from the river Kibe. In Hamburg, in 1892, the water was fur- nished directly to consumers without filtration; in Altona, on the other hand, the water had been for a number of years filtered. The Hamburg supplv was drawn from the river at a point where there was com- paratively little pollution, but the Altona supply was drawn from the Kibe immediately after the stream had received the sewage f the entire pharmacy viagra cheap population of Ham- burg, numbering nearly light hundred thousand. As .a matter of fact, cholera bacteria were discovered in the Kibe water below the main outlet of the Hamburg sewers. There was every reason to expect, therefore, that the cholera would have been more virulent in Altona than in Hamburg, but the contrary was the case. For a number of years the city of Lawrence in Mas- sachusetts had suffered from typhoid pharmacy viagra cheap fever pharmacy viagra cheap to an unu- sual degree, lor the six years from 1887 to 1S92 the deaths from typhoid fever in that city averaged fifty annually, a proportion of one hundred and nineteen per hundred thousand of population. In 1S93 the drinking-water, drawn from the Merrimac River, was subjected to filtration, and at once the typhoid death rate began to fall. In 1895, pharmacy viagra cheap two years after the filtered water had been in general use in the city, the number of deaths had fallen to sixteen, of which nine occurred among operatives working in certain mills, where un- filtered river pharmacy viagra cheap water was used for washing-purposes, and was also used for drinking by the operatives, because it was more accessible than the city water. In two cases the disease was believed to have been imported, and in five the origin was not accounted for.