434 DR. S. F. HARMER ON THE 



a disastrous fire destroyed a lai-ge part of the city of Hamburg, 

 including the buildings which contained the machinery of several 

 distributions of water. The Municipality thereupon took ovei 

 the supply of water ; and it is satisfactory to learn that the 

 English Engineer, Lindley, Avho is described as the author of the 

 project, insisted on having an installation of sand-filtei'S. Partly 

 owing to financial difiiculties, and partly in consequence of the 

 objections raised by the manufacturers and vendors of domestic 

 filters, Lindley's recommendation was not followed for many 

 years, x^t last, however, the difiiculties were overcome, and the 

 construction of filters, which were to be completed in 1894, liad 

 commenced in 1890. Shortly after this date the water taken 

 from the Elbe became contaminated by a temporary encampment 

 of Russian emigrants, and cholera broke out in August 1892, 

 before the completion of the new works. This epidemic, which 

 claimed 10,000 victims, was clearly traced to the defect in the 

 water-supply, since the neighbouring town of Altona, which took 

 its water from the same source but filtered it before using it, 

 i-emained unaffected. The cases which actually occurred in 

 Altona were traced to the use of Hamburg water ; while blocks 

 of houses in Hamburg which were supplied from Altona escaped 

 infection. Mr. S. 0. Chapman informs me that he has heard 

 from Professor Kraepelin that the introduction of filtration, 

 " through extensive gi^avel-beds," was almost immediately suc- 

 cessful at Hamburg ; the pipe-fauna dying from starvation in 

 the course of a few months after the installation of the filters. 



It might naturally be anticipated that the conditions in the 

 reservoirs and filter-beds (in the layer of water above the sand) 

 would be favourable for the growth of numerous freshwater 

 organisms. These are the sources from which the pipes may 

 become colonised, if not protected by filters ; and it is thus of 

 interest to notice that the facts are in accordance with expectation. 

 A case of this kind is recorded by Hickson (04, p. 675), where 

 great ti'ouble was caused in the supply of the town of Burnley 

 by the occurrence of enormous numbers of Lhnncea peregra 

 in the Hecknest reservoir. An even more striking instance is 

 described by Kemna (99, pp. 47, 48) from his own experience 

 in the Antwerp reservoirs, in 1896. In this case the trouble 

 was caused by the extraordinary multiplication of Gladocera., 

 which were so numerous that it was necessary to strain all the 

 water passing to the filters through screens of wire-gauze. So 

 great was the number of these small Crustacea that it was found 

 necessary to keep six men constantly employed, night and day, 

 in changing the strainers. The quantity of Crustacea thus 

 removed was estimated by Kemna at ten tons at least. 



Another striking case, due, however, to defective construction 

 of the filters, is the one recorded by De Yries (90, pp. 56 et seq.), 

 where enormous numbers of Gani'marus and Asellus occurred in 

 the filter-beds and other parts of the system. 



It need not be a matter for surprise if a particular system should 

 be found to have been free from trouble due to Polyzoa and other 



