In addition to affecting a reduction in the typhoid death rate, Mills and Reincke noted (Mills-Reincke phenomenon) that following the improvement in a water supply by the introduc tion of purification processes, there is not only a drop in the typhoid death rate, but a drop in the general death rate as well. From studies by McLaughlin it would appear this decline is due to a decrease in infantile deaths from diarrhea.
The type of purification process or processes best adapted to a given source of water supply, as well as the source of a con templated municipal supply itself, had best be selected by competent sanitary engineers after careful study has been made of the source, its prob'able ability to supply the demands of a growing population for the next twenty or thirty years and the character of the impurities whose removal is necessary.
g. Domestic Water Supplies (Figs. 44, 45, 47) .—These include wells, springs, and cisterns. It is important to remember that with these the danger of contamination is practically exclusively from surfaces sources. They should therefore be protected from surface drainage, and have tight water-proof tops. They should also be located a considerable distance
from sewers, privies and cess pools. Underground contamina tion may occur in clayey or gravely soils or in limestone regions, owing to the fissured or open character of the sub-soil. Shallow wells are frequently contaminated.
1o. Emergency Protection in the various do mestic filters are of little value, as in order to give satisfactory results they must be cleaned freauentiv. at least daily. and it is rare for them to receive this care. They are apt to give a false sense of security.
Boiling drinking water from 15 to 20 minutes is one of the best emergency safeguards that can be employed. Another method of equal value is the employment of bleach or chlori nated lime. A stock solution of bleach is made by adding one teaspoonful of fresh chlorinated lime to a pint of water. • This is added to the drinking water in the proportion of one teaspoonful to ten gallons, or nine drops to one quart, and allowed to act for 15 to 3o minutes before the water is consumed.