Report on the Bacteriology of Water. 



195 



subsequently ? And, what relations subsist between the facts eluci- 

 dated and the questions concerned in our enquiry ? 



The purity of the subterranean waters is certainly not due directly 

 to the rain which falls on the land (and which is, of course, the 

 original source of such waters) being devoid of germs ; because, in the 

 first place, much of this rain is already contaminated before it touches 

 the soil, by bacteria suspended in the air, and secondly, because the 

 instant that the rain touches any ordinary soil it becomes abundantly 

 contaminated with micro-organisms. 



So long as this water is near the surface of the soil, it forms, in 

 fact, a medium admirably adapted for the growth and multiplication 

 of the myriads of Schizomycetes and other organisms with which the 

 surface soil teems. 



It is this surface water flowing off the land into our rivers, open 

 wells, &c, which so abundantly contaminates them by carrying with 

 it, not only the microbes themselves, but also the soluble organic and 

 mineral matters which serve them as food materials.* 



As the rain water percolates into the land, however, more or less 

 of it soon sinks to levels below those at which there is danger of its 

 emerging as a contaminating fluid, and in this process of percolation 

 two important changes take place. Firstly, as the water passes from 

 the surface soil to the sub-soil, it leaves behind it both soluble and 

 suspended matters : certain of its salts are retained in the films on 

 the surfaces of the particles of earth, whilst other salts become dis- 

 solved in it ; it is also, to a great extent, deprived of its dissolved 

 oxygen, and a large proportion of its suspended germs are held back 

 in the capillary interspaces. t In the subsoil, the water is in contact 

 with Schizomycetes of quite different nature from those in the well- 

 aerated surface soil, rich in organic and other food materials, and 

 although these anaerobic organisms of the deeper layers are not 

 necessarily less injurious, or otherwise, than the aerobic forms in the 



* See especially two admirable renews by Duclaux, in ' Ann. de l'lnst. Pasteur,' 

 vol. 4, 1890, on " Le Filtrage des Eaux," pp. 41 — 56; and " Sur les Relations du Sol 

 et de l'Eau qui le traverse," pp. 172 — 184. 



f Of the extraordinary power possessed by even thin strata of suitable filtering 

 materials of arresting microbes present in the water passing through them abundant 

 evidence has been furnished by one of us (Percy P. Frankland, " On the Eemoval 

 of Micro-organisms from Water," 'Roy. Soc. Proc.,' 1885), as well as by Hesse 

 (" Ueber Wasserfiltration," ' Zeitschr. f . Hygiene,' 1, 1886, p. 178), Pohl (" TJeber 

 Filtration d. Newa-wassers," ' Centralbl. f. Bakteriologie,' 1, 1887, p. 231), Bert- 

 schinger (" Untersuchungen uber die "Wirkung d. Sandfilter d. Stadtischen Wasser- 

 werke in Zurich," ' Vierteljahrsch. d. Naturforsch. Gresellschaft in Zurich,' 34, 1889), 

 C. Fraenkel and C. Piefke (" Yersuche uber die Leistungen d. Sandfiltration," 

 'Zeitsch. f. Hygiene,' 8, 1890, p. 1), C. Piefke (" Aphorismen uber Wasserversor- 

 gung, Einrichtung und Betrieb von Filteranlagen," ' Zeitsch. f . Hygiene,' 8, 1890, 

 p. 331), Proskauer (" Die Reinigung v. Schmutzwassern nach dem System Schwarz- 

 kopf," ' Zeitschr. f. Hygiene,' 10, 1891, p. 51). See our Appendix A. 



