Berkefeld Filter
In Position for Filtration of Water to be Examined. sterile brush the particulate matter on the candle of the filter is brushed off into 10 or 15 cc. of sterilised water. This simple arrangement is analogous to the use of gravity or centrifugal methods of securing the solid matter in milk. The smaller quantity of water is then readily examined, and scanty germs more readily detected. A second point elaborating the scheme of water examination is the choice of media for sub-culturing. Mere examination on gelatine is not sufficient. Even in making the primary plate cultivations it is well to vary the media—agar, carbol-gelatine, Elsner, etc. But when colonies have appeared upon these plates it is important to sub-culture with accuracy and good judgment upon all or any media—gelatine, agar, broth, potato, milk, blood serum, glucose agar, glycerine agar, etc.—that will reveal the real characters of the bacteria present. A method proposed by Professor Sheridan Delépine is to place some of the suspected water in sterilised test-tubes without further treatment, and incubate at 37° C. for twelve or eighteen hours, and then plate out and estimate the number of bacteria as in the ordinary course. "In polluted water, containing an excess of organic matter," he says, "an extremely rapid multiplication of bacteria is observed. In unpolluted water, containing only water bacteria and a very small amount of organic matter, very little or no multiplication takes place, and the growth of the water bacteria liquefying gelatine is checked to a remarkable extent." Thirdly, by none of these methods should we be able to isolate anaërobic bacteria, and to furnish a complete report these also must receive careful attention.
Apparatus for Filtering Water to Facilitate its Bacteriological Examination
The Bacteriology of Water. In many natural waters there will be found varied contents even in regard to flora alone: algæ, diatoms, spirogyræ, desmids, and all sorts of vegetable detritus. Many of these organisms are held responsible for divers disagreeable tastes and odours. The colour of a water may also be due to similar causes. Dr. Garrett, of Cheltenham, has recorded the occurrence of redness of water owing to a growth of Crenothrix polyspora, and many other similar cases make it evident that not unfrequently great changes may be produced in water by contained microscopic vegetation.
With the exception of water from springs and deep wells, all unfiltered natural waters contain numbers of bacteria. The actual number roughly depends upon the amount of organic pabulum present, and upon certain physical conditions of the water. As we have already seen, bacteria multiply with enormous rapidity. In some species multiplication does not appear to depend on the presence of much organic matter, and, indeed, some can live and multiply in sterilised water: Micrococcus aquatilis and Bacillus erythrosporus. Again, others depend not upon the quantity of organic matter, but upon its quality. And frequently in a water of a high degree of organic pollution it will be found that bacteria have been restrained in their development by the competition of other species monopolising the pabulum. Probably at least one hundred different species of non-pathogenic organisms have been isolated from water. Some species are constantly occurring, and are present in almost all natural waters. Amongst such are B. liquefaciens, B. fluorescens liq., B. fluorescens non-liquefaciens, B. termo, B. aquatilis, B. ubiquitus, and not a few micrococci, etc. Percy Frankland[14] collected water from various quarters at various times and seasons, and some of his results may here be added:
RIVER THAMES WATER COLLECTED AT HAMPTON
Number of Micro-organisms Obtained from 1 cc. of Water.
| Month. | 1886. | 1887. | 1888. |
| January | 45,000 | 30,800 | 92,000 |
| February | 15,800 | 6,700 | 40,000 |
| March | 11,415 | 30,900 | 66,000 |
| April | 12,250 | 52,100 | 13,000 |
| May | 4,800 | 2,100 | 1,900 |
| June | 8,300 | 2,200 | 3,500 |
| July | 3,000 | 2,500 | 1,070 |
| August | 6,100 | 7,200 | 3,000 |
| September | 8,400 | 16,700 | 1,740 |
| October | 8,600 | 6,700 | 1,130 |
| November | 56,000 | 81,000 | 11,700 |
| December | 63,000 | 19,000 | 10,600 |