382 



Dr. P. F. Frankland. 



[June 18, 



a thin layer of asbestos. Before use, the filter thus prepared was 

 sterilised by heating it to a temperature above 150° C. for at least 

 three hours. After sterilisation the filter was at once put in opera- 

 tion by supplying the infected water at the wide end of the tube, the 

 filtered water being collected when required in a vessel sterilised in 

 the same way beneath the lower extremity of the tube. In those 

 experiments in which the filtration was carried on for many days, or 

 even weeks, the infected water was constantly supplied to the filter 

 by means of an inverted flask fitted with a delivery-tube, the latter 

 dipping into the water above the filtering material. The following 

 results were obtained with the various materials : — 



Greensand. — The urinous water passed through this filter, on start- 

 ing, at the rate of 2'07 inches per hour. The sand was highly ferru- 

 ginous, and the filtered water contained a noticeable proportion of 

 iron. 



On examining the unfiltered water, it was found to contain 64 centres 

 of life in one, and 97 centres per c.c. in a duplicate experiment ; these 

 consisted almost wholly of organisms causing liquefaction of gelatine, 

 a few fungi, and the remainder small spherical colonies. In the 

 filtered water, on the other hand, there were no organisms of any 

 description discoverable. The filtration had thus completely sterilised 

 the water. 



In order to ascertain whether the greensand would continue to 

 exercise this influence, the arrangement for continuous filtration, as 

 already described, was put in operation, and after being in action for 

 thirteen days, during which time 7*1 litres of water passed through, 

 the efficiency of the filter was again tested. The unfiltered urine- 

 water was found to contain 8193 centres per c.c. The filtered water 

 was found to contain 1071 centres per c.c. These experiments show 

 that although the original power of the greensand was broken down, 

 the filter was still arresting a considerable proportion of the organisms 

 present in the water passing through it. 



The efficiency of the filter was again determined after the con- 

 tinuous filtration had proceeded for one month, when 20 litres of 

 water had passed through. The following results were obtained : — 



The unfiltered water contained . . 1281 centres per c.c. 

 The filtered „ „ .. 779 „ „ 



On the whole, therefore, even after the lapse of an entire month, a 

 notable proportion of the organisms was still being removed by the 

 greensand filter. 



Animal Charcoal. — Perfectly similar experiments were made with 

 this well-known filtering material. On examining the initial efficiency 

 of the filter, it was found that whereas the unfiltered water contained 

 so many organisms that the gelatine on the plates had become entirely 



