isms." As a rule they are said to be quite uninjurious to health, but when occurring in enormous numbers, it is no wonder that people speak of them as they did in Berlin when a severe visitation of Crenothrix was pronounced a "water calamity."

It is only within recent years that biologists have systematically studied the microscopical organisms, and it is worthy of note that their study has been greatly stimulated by engineers who have appreciated their importance. From 1675, when Leeuwenhoek first observed "animalcula in pepper water," to the middle of the present century, they were studied solely from the botanical and zoological standpoints. Thousands of species were named and classified. In 1850 Dr. Hassall, of London, pointed out the practical sanitary value of microscopical examinations of water. His suggestions were taken up by various workers in England and Germany, but for more than a quarter of a century there was little done to perfect the method, which consisted merely in the examination of the sediment deposited from a sample of water in a suitable jar. Since 1888 the sanitary study of the microscopical organisms has been pursued with more diligence on this side of the Atlantic. Numerous improvements have been made in the methods of examination, culminating in what is known as the Sedgwick-Rafter Method. This consists in determining quantitatively the number of organisms in a sample of water by collecting them on a sand filter and subsequently transferring them in a little water to a suitable cell and counting them under the microscope. This method has been of great

service in extending our information concerning the living organisms in drinking waters, and we appreciate their importance as never before. The extensive series of biological examinations made by the Massachusetts State Board of Health, by the Boston Water Works, and by others, have been of much practical benefit. It is now known that ground water must not be stored in open reservoirs, but must be kept in the dark to prevent the growth of algae, which is almost sure to be stimulated by exposure to sunlight. It has been shown that in order to store surface water safely the reservoirs must be clean. Engineers have been a long time in coming to realize this, but it is now generally accepted by the best authorities that in constructing a reservoir it is absolutely essential to remove all the organic matter of the soil likely to be covered by the water. Biological studies have also shown that it is necessary to properly drain the swamp areas that occur within the watershed of most surface supplies, because they are active breeding places for troublesome organisms. Our knowledge regarding the seasonal occurrence of these organisms is being greatly extended, and we shall soon know better how to manage certain supplies in order to get at all times the best water possible. We are also learning which of the organisms are likely to cause trouble and the number that may be present in a water without producing bad effects.

It is not only in connection with questions of water supply that biology has been of service to the engineer. It has been equally useful in helping to solve the problems of sewage disposal. The old practice of

allowing the sewers to empty their vile contents into the nearest pond or stream is gradually being abandoned, and in its stead some form of chemical treatment or some system of filtration is beginning to be used.

Great advances have recently been made in the ideas regarding sewage filtration. It was first supposed that the ground acted as a strainer to remove the solid particles and very fine sand or loam was thought to be the most efficient material. Then it was said that the action was one of oxidation within the pores of the filter. This was nearer the truth; but it remained for the biologist to provide the true theory, namely, that purification is chiefly effected through the action of bacteria which establish themselves in the filter upon the sand grains. The magnificent series of experiments which has been carried on at the Experimental Station of the Massachusetts State Board of Health has thrown a flood of light upon the theory of sand filtration as well as its practical application. It has been found that a filter must be treated not as a strainer, but as an immense colony of organisms whose one object in life is to convert the decomposable matter of the sewage into harmless nitrates. These organisms must be given their food regularly and in definite quantities; they must be given a certain amount of oxygen and a certain amount of time in which to do their work-these factors all depending upon the character of the sewage filtered and the composition and amount of the sand used. Properly treated, a filter will continue to do its work faithfully for a long period. It cannot, however, be trifled

with. It must not only be properly constructed, it must constantly receive the faithful attention of one who understands its nature and the needs of the bacteria which dwell within its pores.

The science of bacteriology has touched the engineering profession at other points which need not be specified. What is most important of all, it has caused a tremendous uplift of public sentiment in favor of better sanitation everywhere. Better plumbing, better ventilation of buildings, better methods of disposal of all sorts of waste material, better care of streets, are all being demanded by an enlightened public.

All this means more work and greater responsibilities for the civil engineer. He is the one who must carry out the reforms; he must see that the work is properly designed and carefully executed. Such a man upon whom depends the expenditure of vast sums of money, and even the fate of human lives, needs to be broadly and deeply educated. In this age of bacteria he should have at least some knowledge of biologyenough to enable him to properly appreciate the nature of the problems of water and sewerage work, and to co-operate intelligently with expert sanitarians in their solution. He need not be able to make a chemical or a biological analysis, but he ought to know how to interpret one and how to make it of practical use; he need not know how to make a pure culture of Bacillus typhosus or how to distinguish it from Bacillus coli communis, but he ought to know how typhoid fever is transmitted and what measures should be adopted to protect a community from its ravages; he

need not know the names of all the micro-organisms and their proper classification, but he will find it of advantage to know the characteristics of the most troublesome forms that occur in drinking water.

In ordinary practice, cases frequently occur where the engineer is obliged to act promptly and upon his own responsibility, and where even an elementary knowledge of biology would be of material assistance to him and enable him to avoid serious mistakes. It would also serve to prevent him from being unduly influenced or alarmed by the sensational utterances which are continually appearing in the public press in regard to "the deadly germs." As an illustration of this we may refer to an epidemic of typhoid fever that occurred not long ago in a city not far from Boston. The increasing number of cases caused the usual alarm and the usual number of wild speculations as to its origin. By some of the leading physicians it was attributed to the water supply, and the waterworks officials were much disturbed by it because they were not able to disprove the assertion. For several days they sat upon the anxious seat, when an expert biologist came and easily demonstrated that whatever else might be at fault, the water supply was above suspicion. Soon afterwards a certain milk supply was found to be the cause of the epidemic. If the local engineers had had a better understanding of the theory of the transmission of disease, they might have saved the citizens several days of anxiety and complaint.

A general knowledge of the principles of sanitary biology can be acquired by the engineering student in