First Report to the Water Research Committee of the Royal Society, on the present State of our Knowledge concerning the Bacteriology of Water, with especial reference to the Vitality of Pathogenic Schizomycetes in Water.

By PERCY F. FRANKLAND, Ph.D., B.Sc. (Lond.), F.R.S., Professor of Chemistry in University College, Dundee, and MARSHALL WARD, SC.D., F.R.S., F.L.S., Professor of Botany in the Royal Indian Engineering College, Coopers Hill. Presented to the President and Council, May 19, 1892.

Introduction.

The interest attaching to the presence of micro-organisms in water originated principally in the proof, which has been furnished by medical men, that some zymotic diseases are communicated through drinking water. In the case of two diseases, at any rate, the evidence may be regarded as conclusive on the main point, and the communicability of Asiatic cholera and typhoid fever forms one of the cardinal principles of modern sanitary science, which year by year is becoming more widely recognised and generally accepted. The germ theory of zymotic disease, which has become more and more firmly established during each successive decade of the past half century, was naturally soon impressed into the service of those who sought to explain the empirical fact that these particular diseases are frequently communicated by water. It is significant that these views concerning the propagation of cholera and typhoid, and the importance to be, therefore, attached to drinking water in connexion with public health, are mainly English in origin, and were for many years unflinchingly preached and practised by English sanitary authorities, at a time when the germ theory of disease was a speculation, and not established as it now is. It is only necessary to read, by the light of our knowledge of to-day, the Sixth Report of the RiversPollution Commissioners (1868), written more than eighteen years ago, to be convinced of the intuitive sagacity and acumen which has been displayed in this country in matters of sanitation.

The germ theory of disease having thus so early become interwoven with the consideration of potable waters, it is easy to understand with what eager interest the vigorous development in our knowledge of micro-organisms in general, and of their connexion with

VOL. LI.

disease in particular, which has taken place within the past fifteen years, has been watched by those who have had to devote much attention to the sanitary aspects of water-supply.

The subject of our particular enquiry is, therefore, a modern one, and may be regarded as having been made amenable to successful treatment by the introduction of Koch's method of gelatine-plate cultures in 1881, and subsequent improvements on the same.*

The publication by Koch of his beautiful and comparatively simple methods of bacteriological study gave an impulse to this kind of work throughout the civilised world. These methods, in spite of certain imperfections from which they never professed to be free, at once opened up the possibility of solving a number of problems connected with water-supply which had long been matters of dispute and speculation amongst hygienic authorities.

As is now well known, Koch's method of gelatine-plate culture admits of an estimate being made of the number of living germs present in a given quantity of any material. That this estimate is a very rough one, and that there are a number of different kinds of germs which it is incapable of revealing, was also known, and has been more or less admitted from the outset. Now this possibility of estimating the number of microbes in a given volume of water has been largely made use of by numerous investigators for a number of different purposes.

In the first instance, this method has been extensively employed both in this country and abroad for determining the relative richness in micro-organisms (capable of developing in gelatine) of various natural waters. On the Continent, and more especially in Germany, it was assumed that the relative numbers of microbes present in different waters afforded evidence of the extent to which they had been contaminated, and there were not wanting those who hastily set up arbitrary standards of purity based upon a most limited experience of the number of micro-organisms revealed by the gelatine test. By those who were simultaneously employing the method in this country

Koch's first announcement of his new method was made at the meeting of the International Medical Congress in London, in August, 1881 (see 'Quart. Journ. Microsc. Sc.,' Oct., 1881, p. 650), and then published in the 'Mitth. aus d. K. Gesundheitsamte,' vol. 1, 1881 (see also ' Berl. Klin. Wochenschr.,' 1882, No. 5). It should be noted, however, that Koch's gelatine-plate method was an improved adaptation of one introduced long before by the botanists Brefeld and Klebs (see Brefeld, "Methoden zur Unters. der Pilze," Abh. der Phys.-Med. Gesellsch. in Würzburg,' 1874; also Landwirthsch. Jahrb.,' vol. 4, H. 1, and 'Unters. über Schimmelpilze,' 1881, H. 4; also Klebs, "Beitr. zur Kenntn. d. Mikrokokken," Arch. für exp. Pathol.,' vol. 1, 1873, and De Bary, Lectures on Bacteria,' Engl. ed., 1887, p. 35). A fair view of the matter is given by Hueppe, 'Die Methoden der Bakterien-Forschung,' 1885, p. 103. To Koch belongs the credit of having applied these plates to the purpose of separating the various colonies of mixtures of micro-organisms.

more caution and reserve were exercised in this respect, the results being tentatively chronicled without comment or deduction as to purity.

The prudence of this caution was soon apparent, when both in England and in Germany it was discovered in 1885 that many forms of micro-organisms could multiply to an astonishing extent in waters of great organic purity, including distilled water itself. It is obvious that this discovery at once subverted the artificial standards which had been proposed, for, although a small number of micro-organisms might frequently point to little or no contamination having taken place, a large number could only under special circumstances be viewed as conclusive evidence of proportionate contamination.

Another question was, however, being simultaneously attacked, both in this country and on the Continent, viz., the effect of various processes of purification on the bacterial life present in water. This question, which is of evident importance, could be investigated with considerable precision by means of the gelatine-plate method, in spite of its imperfections, for by applying the same mode of culture to a particular water before and after purification, it is obvious that the defects neutralise each other, and that a true differential result can be obtained. In this manner, the value of a number of filtering materials has been ascertained, and the remarkable efficiency of water-works sand-filtration for the first time established. Again, the fact that practically all surface waters exhibit a large number of microbes by the gelatine test, whilst deep well and spring waters yield very few, or in some cases none, shows how perfect, as regards removal of micro-organisms, must be the natural filtration which water undergoes in traversing great depths of porous strata in the earth.

It has also been shown that in the subsidence of solid particles often a surprisingly large proportion of the micro-organisms present in water are carried to the bottom, a matter which is of particular interest and importance in connexion with the natural purification of surface waters in rivers, lakes, and storage reservoirs, as well as in the artificial treatment of water-supplies by Clark's softening process, and other methods of precipitation. In applying the gelatine test to these various purification processes it is, however, essential, if an accurate result is to be obtained, that the water should be examined immediately (within a few hours) after the purification is completed, and before the number of microbes in the purified. water can have multiplied naturally.

Another use to which the bacteriological methods have been applied is to the actual discovery of pathogenic microbes in water, and, in the opinion of some, this should indeed be the primary object of bacteriology in connexion with water-supply. This view appears