Hygiene and public health / by Louis Parkes and Henry Kenwood.

  • Parkes, Louis Coltman, 1857-1942.
Date:
1901
Catalogue details

Licence: In copyright

Credit: Hygiene and public health / by Louis Parkes and Henry Kenwood. 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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    or tank, should always be railed off to keep live stock away. The surface of a certain area of land in an exposed situa- tion is rendered impermeable by a covering of slates, asphalte, or cement, and sloped towards an outlet pipe or pipes leading to a tank or reservoir. In estimating the amount of water that can be obtained from such a surface, calculations may be facilitated by remembering that one inch of rain delivers 4-673 gallons on every square yard, or 22,617 gallons (loi tons) on each acre. Rain, as it leaves the clouds, is water pure and simple, free from all foreign ingredients. In its passage through the air to the earth it may collect various impurities— gaseous and suspended. The rain falling in towns is found to have absorbed sulphurous and sulphuric acids, always present in the air of towns from combustion of coal and coal gas, and to contain numerous sooty particles. From the observations made at Montsouris, near Paris, by Dr. Miquel, it also appears that the rain washes out of the air countless bacterial and fungoid organisms and their spores. The rain which first falls in a shower, and that which falls after a period of dry weather, contains far larger numbers of bacteria than that which falls later on in a storm, or succeeds the first shower; 200,000 germs per litre is not an unusual quantity under the first set of circumstances. During the warm months of the year, the number of bacteria in the rain are greatly in excess of those found in the rain falUng in winter and early spring. The greater number of the organisms in rain are micrococci. All the organisms found in rain exist to a larger extent in the form of spores than in the adult state. Besides bacteria, pollen of grasses and flowers, inicroscopic plants such as Protococcns phivialis, and spores of fungi are occasionally found in rain, the latter being on rare occasions in sufficient quantity to