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.

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.

Studying the causes of death among inhabitants in mountain villages located alongside the middle stream of the Tenryu River, and farming-fishing villages located along Tokyo Bay, we found that the death rate from lung cancer was high in the former, and that from stomach cancer was high in the latter. So, in those two districts, we carried out case-control studies about both kinds of cancer. Investigation was made into the dead cases from lung cancer, 84 male cases and 168 male controls, and the dead cases from stomach cancer, 83 male and 39 female cases and the same number of controls. We selected these controls, matching district, sex, age, and year of death, and studied occupation and smoking in lung cancer cases ; occupation, eating habits, kinds of food, drinking and smoking in stomach cancer cases. The odds ratio concerning to lung cancer was as low as 0.40 among people engaged in agriculture, forestry or fishery. But that was as high as 3.25 among people exposed to metal dust, and also as high as 3.10 among those exposed to wood dust. The multiplier effect could be suggested between smoking and metal or wood dust exposure. The odds ratio concerning to stomach cancer was as low as 0.69 among males engaged in agriculture, forestry or fishery. Regarding eating habits, ‘rapid eating’ was as high as 2.57 in males, 3.00 in females. Concerning the kinds of food, ‘salted fish’ was as high as 1.90 in males, and ‘white vegetables’ was as low as 0.36 in females. No assocciation was found between stomach cancer and smoking or drinking.