BY THE HON. W. F. TAYLOR, M.D., ETC. 53 



upper layers of the filtering medium, but the numbers kept on 

 increasing, owing to the organisms which were retained in the 

 filtering medium having undergone multiplication, and some of 

 those arrested from previous charges, being washed down. On 

 the fourth day of testing the filters, the results were in the case of 

 every filter tried, an enormous increase of micro-organisms. 



It is clear, from these experiments, that the ordinary filter 

 not only does not intercept micro-organisms, but after a short 

 time of use, adds very materially to their number in the filtrate. 

 If they will not arrest micro-organisms, it is hardly to be sup- 

 posed that they will arrest disease germs, and in fact it was 

 proved that they do not arrest them. Not one of these filters 

 was able to arrest the passage of the Staphylococcus pyogenes 

 aureus, yeasts, the cholera or typhoid bacillus ; so that as a pro- 

 tection against water-borne disease they are valueless. It is true 

 that a sterilised filter will, for the first day or two, arrest the 

 greater portion if not all the micro-organisms present in the tap 

 water passed through it, so that to be of any use even in this 

 respect, it should be freshly charged with a sterilised charge of 

 filtering material every second day — a proceeding which would 

 be both costly and troublesome. 



Three filters, however, were found by Drs. Woodhead and 

 Wood, capable of resisting the passage of disease germs. These 

 are the Chamberland Pasteur Filter, the Berkefeld Filter, and 

 the Aeri-Filtre-Mallie Porcelaine D'Amiante. The first con- 

 sists of a filtering machine composed of a specially prepared 

 form of porcelain formed by a mixture of kaolin and other clays, 

 the exact details of which remain a trade secret. These filters 

 are supplied in two forms — as table filters, and tap or pressure 

 filters — the latter being the form most commonly used, for on 

 account of the density of the porcelain forming the candles or 

 filtering medium, filtration is very slow unless under considerable 

 pressure. The table filter when composed of only one candle, 

 requires such a long time to filter sufficient water for ordinary 

 use, that it is found necessary to group together two or more 

 oandles to render it of much value. The only sample of this 

 form of filter that I have yet seen is the one I hold in my hand, 

 and which comes from the Stock Institute here — Mr. Pound 

 having kindly lent it to me for this evening. It is a hollow 



