The outstanding feature of the drift of population observed in our country of late is understood in terms of the population exodus from rural areas into urban or industrial areas, which brings about. a conspicuous decrease in rural population especially in that of the younger working age bracket. with a view to clarifying an aspect of such wide-ranging migration of population, a study was made in the three remote mountain villages in the Chilbu District, where people are living on an extremely low economic level Investigation conducted for eacch respective economic level revealed an even. abnormally advanced decrease in the population of such younger generation, far advanced than in average rural areas. Thus the unfavorable topogra-phical conditions, lack of cultivating lands, low income, etc.were considered to be responsible for the acceleration of such population exodus. Attention was also drawn to the fact that not only the surplus labor power but even many of the eldest sons. who are the successors to their fathers' occupations are turning to urban areas for employ-ment, threatening the possibility of the replenishment of agricultural labor power and the development of agricultural economics, as well as the future reproduction of population in rural areas.

In the five communities of Urakawa, Sakuma-machi, Shizuoka Prefecture, we have taken measures to Prevent and exterminate ascaris infection, and at the same time studied the causes of infection chiefly from the point of view of environmental conditions. The percentages of ascaris egg-carriers showed a significant difference between 1) farmers and non-farmers; 2) families with and without night-soil; 3) amounts of detergent used for cleaning vegetables; 4) persons with and without experience of anthelmintic treatment.
The group of families that showed extremely high rate of positivity were the farmers not provided with night-soil stores, and the farmers provided with such stores showed about the same rate of positivity as non farmers a fact evidences the appreciatng effect of night-soil stores. On the other hand, the rate of positivity among familis that have no night-soil stores but are in the habit of cleaning vegetables with detergent showed no significant difference as compared with the families provided with night-soil storesa positive evidence of the good effect of detergent.