“…In general, all of the facts and observations on the manner of occurrence and the distribution of cases in time, place and persons must be consistent with the hypothesis of dissemination by the suspected water distribution system and no other explanation must be equally valid. It consists very largely of observations on the occurrence of groups of cases along watercourses (lakes, rivers and brooks) into which sewage is discharged, and of Kling's belief-based upon the 1942 laboratory experiments of Carlson, Ridenour and McKhann (21) to which reference has been made above-that the treatment of these surface waters by filtration through sand (no details given), which was satisfactory by bacteriological tests, was insufficient to remove viruses. In the six years which have elapsed since that publication there have been numerous reports of investigations of the occurrence of poliomyelitis in various areas of this country and in other parts of the world.…”