latter year Löffler found the bacillus of diphtheria and Gaffky published his researches in regard to typhoid fever. These results were of great practical value and furnished sanitarians with a sound working basis. It was self-evident that if the bacteria were the cause of disease they must be kept out of the body. A new stimulus was, therefore, given to the study of the nature of the bacteria in food and water.

In 1885, Dr. P. F. Frankland used the Koch plate method in the examination of the water of the London filters, and even before that Koch himself had used his method in examining some of the German water supplies. Here for the first time bacteriology was made to serve the engineer. The character of a water supply or the efficiency of a filter could now be determined as never before. It must have been indeed gratifying to those who constructed the early filters in England to learn that 95 to 98 per cent. of the bacteria were being removed from the water. The results of analysis, however, showed that there was still room for improvement.

Bacteriology has shown that the terrible epidemics of cholera and kindred diseases, which in times past have swept over Europe and which have sometimes threatened to invade America, may be prevented. It has shown how the germs of these diseases are often water-borne and how essential it is for communities to be supplied with water free from any suspicion of pollution. It has shown how this may be accomplished by means of proper filtration. filtration. Filters now in operation have given practical proof of their efficiency. Perhaps no better example can be cited than the ex

perience of two German cities during the recent outbreak of cholera.

The cities of Hamburg and Altona, situated on the Elbe river, are so close together as to be practically one. There is no natural boundary between them. In 1892, when the cholera epidemic threatened all of Europe, both cities drew their water supply from the river. The water supplied to Altona was filtered with great care, but the Hamburg filters were not completed and the city was served with raw water somewhat improved by sedimentation. The different behavior of these two cities with reference to the cholera was remarkable. We all remember how severely Hamburg suffered and how, out of a population of 640,000, 17,000 were stricken with the disease. In Altona, with a population of 143,000, there were not over 700 cases and many of these originated in Hamburg. Prof. Koch, in describing the epidemic, said, "Cholera in Hamburg went right up to the boundary of Altona and there stopped. In one street which for a long way forms the boundary, there was cholera on the Hamburg side, whereas the Altona side was free from from it."

But we need not go abroad to find examples of the protection which a properly filtered water supply gives to a community against the invasion of waterborne diseases. The city of Lawrence, Mass., situated upon the Merrimac river and utilizing this polluted stream as a source of water supply, suffered for many years from autumn epidemics of typhoid fever. In 1892 the city constructed what is perhaps the most scientifically designed filter in existence.

Soon after it had been put into use, bacteriological examination of the purified water showed an almost entire absence of bacteria. The immediate and remarkable decrease in the death rate from typhoid fever after the installation of the filter, stands as a splendid triumph of modern science and as a striking example of what the sanitary engineer of the future is to accomplish.

If such results are possible in Altona and Lawrence, they are possible elsewhere, and it is to be hoped that the day is not far distant when no community will be content to be served with drinking water that has not been filtered or otherwise purified. It will sometime be considered as much an act of barbarity to drink unpurified water as to eat uncooked food. We used to hear a good deal about the theory that "running water will purify itself," and acting upon this theory it was considered safe to utilize a river both as a place of disposal for sewage and as a water supply for domestic purposes, provided that the outlet of the one was several miles removed from the intake of the other. Bacteriological studies have exploded that theory and we must now look upon the use of such a polluted water not so much as an error of judgment, but rather as a crime against the community.

For a long time to come, however, it is probable that many of our cities will continue to use surface water stored in natural ponds or artificial reservoirs without filtration. Even with filtration, storage reservoirs will be found necessary. The question of storing water is, therefore, one which must receive the

careful attention of the engineer and it is one upon which biology can offer him great assistance.

Water is never found chemically pure in nature. It invariably contains certain substances in solution which are suitable as food for some of the microorganisms, the amount of this food material varying within wide limits. Now the micro-organisms, or their spores, are widely distributed and they are not slow in seizing upon the food supply which the water has abstracted from the soil and placed at their disposal. It is, therefore, not an easy matter to store water and be sure that it will retain its original good qualities. Scores of instances are on record where the water of ponds or reservoirs has become totally unfit for use on account of troublesome organisms. While it is perhaps unnecessary to cite examples of afflicted water supplies, it may not be out of place to refer to a personal experience with an organism hitherto unknown to be one of our enemies and seldom if ever before observed in drinking water.

A few weeks ago the water supplied to one of our New England cities was noticed to have a faint green color as it came from the tap. When a glass of it was held towards the light and examined closely, it was seen to be filled with minute particles. On standing, these particles settled out as a bright green sediment. The water had a slight unpleasant taste and odor but this did not cause much comment. On Monday, however, when people began to use the water for washing, a cry was set up all over the city that the water left green stains on the clothes. Before noon samples of stained clothing began to appear at the

office of the Water Board and it was evident that the matter needed investigation. The city takes its supply from several artificial ponds which are so arranged that they may be drawn upon singly or in pairs. At the time of the trouble the water was being drawn from the pond which has always been the worst offender in supplying objectionable organisms. This water was at once shut off and a series of samples was collected from all the ponds to locate the nature and extent of the trouble. Strangely enough the samples contained very few organisms, and the water of the suspected pond was particularly free from them. The writer, in company with the superintendent of the water works, then made a personal inspection of the sources of the supply, and was successful in locating the cause of the trouble. The water of the suspected pond, instead of being carried to the city all the way through pipes, flows for a part of its course through an open canal. At the time of our visit the water in this canal was found to be swarming with Raphidomonas, a minute animal form. This infusorian has a bright green color due to the presence of numerous chlorophyl grains and it was this chlorophyl which caused the green stains on the clothes. It was fortunately an easy matter to get rid of the organisms. The canal was emptied at the waste-ways, and the sides and bottom thoroughly cleaned, after which the water was again allowed to run through it. The tap water soon returned to its normal quality.

The organisms which are responsible for most of the bad tastes and odors in water supplies belong to the class above referred to as "microscopical organ