An introduction to the bacteriological examination of water / by W.H. Horrocks.
- Horrocks, W. H. (William Heaton), Sir, 1859-
- Date:
- 1901
Licence: In copyright
Credit: An introduction to the bacteriological examination of water / by W.H. Horrocks. Source: Wellcome Collection.
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![of the colonies are able to develop in the plates. Gelatine plates, however, can rarely be kept under observation beyond the fourth or fifth day, owing to liquefying organisms destroying the plates. Up to the present time the quantitative analyses of most sources of water supply have been made by means of faintly alkaline gelatine-peptone plates, consequently, if it is desired to compaie the results with previous analyses, this medium must be used. The Preparation of “ Water Peates.” The water to be examined should be gently shaken for a few minutes; in this way all clumps of bacteria will be broken u]) and each organism will produce only one colony when it develops in the Petri dish. Forcible shaking of the sample must be avoided as it may cause the death of some of the micro- organisms. The next step is to determine the amount of water which should be used for each plate, as it is necessary that each organism shall have room to develop without touching its neighbours. The simplest method of arriving at an idea of the number of bacteria present in the water is to remove c.c. of the water from the bottle and deposit it on a covei’-glass; then by staining and counting the microbes on the cover-glass preparation it is possible to determine very roughly the number of micro-organisms present in a c.c. of the water. When work- ing with Petri dishes having a diameter of four inches, it is best to use such an amount of water as will give not more than 300 colonies in each plate. If the water contains a very large number of bacteria it must be diluted with sterile tap-watei-. L^sually three plates are made from each sample, containing respectively ^ c.c., ^ c.c. and | c.c. of the water diluted or not as required. In order to measure the calculated amount of water required for each plate, accurately graduated pipettes must be used. One c.c. pipettes graduated in y^^ths are most useful. Each pipette must be thoroughly cleaned, the upper end plugged with cotton-wool, and the lower end placed in a test-tube, the mouth of which is firmly plugged with cotton- wool. The test-tubes and pipettes are then sterilised at 150° C. for three hours and kept in metal boxes until required for use. The Petri dishes, wrapped in thin paper, are also sterilised at the same temperature.](https://iiif.wellcomecollection.org/image/b28116525_0045.jp2/full/800%2C/0/default.jpg)
