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.
Examination of feces and deworming were carried out five times every other month between May 1962 to February 1963 in 5 communities (a total of 202 households, 1, 050 inhabitants) of Urakawa, Sakumamachi, Shizuoka Prefecture. After about a year has elapsed, in which no countermeasures were taken, examination of feces was carried out again in January 1964 to study a change in the rate of positivity. Examination was carried out by the cellophane thick layer smear method (values obtained with two sheets). (1) The rate of positivity for Ascaris eggs ranged from 13.7% to 55.1%, with an average of 28.0% in the initial examination. The rate was higher in two commnities in the mountainous district. By sex and age, the rate was high among infants, school boys and adult females. (2) A study of the change in the rate of positivity during the two years has shown that the rates of reinfection and new infcction were higher in communities where the rate of positivity was higher in the initial examination, indicating how difficult it is to exterminate Ascaris infection. On the contrary, there was no substantial rise in the rate of positivity in communities where the rate of positivity in the initial examination was under 10%(3 out of 5 communities), even though no countermeasures were taken during the period of one year. This seems to show that it is not required to carry out deworming frequently. It has been found that the rate of Ascaris infection was lower in communities where persons positive for unfertilized eggs alone accounted for higher percentages among the total of persons positive for Ascaris eggs, there being a marked inverse corelation between persons positive for unfertilized eggs alone and persons positive for all kinds of Ascaris eggs. There has been a marked tendency to familial concentration of Ascaris infection. (3) The results of the present study have shown that, in taking measures to exterminate Ascaris infection, it is necessary to take into consideration the rate of positivity for Ascaris eggs, the ratio of persons positive for unfertilized Ascaris eggs to persons positive for all kinds of Ascaris eggs, and a tendency to familial concentration of infection in the community.