Disinfection and the preservation of food : together with an account of the chemical substances used as antiseptics and preservatives / By Samuel Rideal.

  • Rideal, Samuel, 1863-1929.
Date:
1903
Catalogue details

Licence: In copyright

Credit: Disinfection and the preservation of food : together with an account of the chemical substances used as antiseptics and preservatives / By Samuel Rideal. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

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    2. Piefke in Berlin, about 1886, found that sterilized sand effected hardly any j^urilication and did not retain microbes. It had previously been noticed that sand filters did not become eflicient for some days after re-laying. 3. When the oxygen or air, and the water were sterilized, little or no oxidation of organic matter occurred. It was proved, therefore, that for the proper mechanical and chemical effects the action of organisms is essential. It must be remembered that some organisms have long flagella, while a large number, such as diatoms and bacteria, are normally surrounded by a gelatinous envelope which greatly increases their size, and enables them to adhere to surfaces, so that in a short time the sand in a new filter becomes covered with a living slimy layer which entangles suspended matters and effects the main part of the purification. This is called schmutzdecke, and sometimes the schlamm- decke, or mud-covering, and until it forms the filtration is inefficient. In the under layers of sand the nitrifying organisms, which work best in the dark, act as they do in soils, causing oxidation, and producing nitrates by the aid of the dissolved oxygen. Green alg^e in their growth evolve oxygen, and so increase the amount in solution, while bacteria as a rule diminish it. Although the chief removal of organisms occurs in the schmutzdecke, the lower layers of sand are not inactive, as Reinsch has shown at Altona. For an example, he gives the average number of organisms per c.c. as :—Raw water, 36,000; just under the schmutzdecke, 1,800; at bottom of sand (35 inches), 44. The proportion of micro-organisms removed by the sand filters of water com.panies shows ordinarily a variation between 95 and 98 5 per cent., but should be well up to the latter figure. Koch laid down as a limit that water contain- ing more than 100 organisms per cubic centimetre must not be allowed to pass into consumption. That when carefully used these filters afford a remarkable protection against pathogenic species, was proved by experience in the cholera epidemic of 1892 at Flamburg and Altona,^ when in Altona the water was filtered carefully, in Hamburg not. Although 'Koch, Zcil. /. Hyg., vol. xiv., p. 393 ; vol. xv., p. 89.