We performed a mass treatment of anchylostomiasis for the inhabitants of four rural villages and for the pupils of two lower-secondary schools in Ichihara-gun, Chiba Prefecture, and obtained the following results:
1. Evaluation of the effect was made 3-4 weeks after the treatment by salt flotation method (plus zinc sulfate) and also by culture. For the salt flotation method two specimens were prepared for each subject. Follow-up examinations were made at regular intervals by the said two methods, and the results were corrected accordingly.
2. Percentages of conversion to negative (i. e. disappearance of both larvae and ova from stool specimens) by different anthelmintics were approximately: 43.5% for tetrachlorethylene, 41.0% for 1-brom naphtol (2), 38.2% for ascaridol-tetrachlorethylene compoundno significant difference was observed among these three drugs; while 14.8% for the compound preparation of ascaridol-tetrachlorethylene-carbonum tetrachloratum and 4.8% for oil of chenopodium. All of these anthelmintics were found more effective for Necator americanus than for Anchylostoma duodenale. And the percentages of conversion to negative were in reverse proportion to the number of worms discharged. Even with the same kind of anthelmintic, percentages of conversion to negative differed with areas where it was administered. Percentages seemed lower in the severely infected villages.
Percentage of cenversion to negative by 1-brom·Enaphtol (2) was lower with smaller doses than with the standard dose for adults (4g.per diem for two consecutive days). There was significant difference between them.
In the mass treatment with tetrachlorethylene, both the percentage of conversion to negative and the appearance of secondary effects were about the same with the group dosed together with laxativa and with the group dosed without it.
3. Delayed effect (i. e. conversion to negative observed by follow-up examinations subsequent to the anthelmintic treatment) occurred to 10.8-17.6% of the cases treated with tetrachlorethylene, to 3.0-11.1% of those treated with 1-brom·Enaphtol (2), and to 14.6%-24.1% of those treated with ascaridol-tetrachlorethylene compound. 78% of such delayed conversion was observed during the four months and 93% during the six months succeeding the treatment. Development of the delayed effect was grasped by monthly counting of ova in stool specimens. The number of ova discharged (E. P. G.& L. P. G.) decreased to half the previous number at each consecutive examination, after the treatment, and in a manner of geometric progress gradually reached zero.

We examined the stool of the 989 prisoners who were serving their time at the Chiba Prison. to see the percentage of anchylostomiasis. on the assumption that the channel of infection should have been cut off for them. The percentage of all the ova positive cases was 12.2. The percentages were in reverse proportion to the length of imprisonment. The relationship between the years of imprisonment (X) and the percentage of ova positive cases (Y) was: Y=19. 12-1. 92X. These positive cases were left untreated for two years.Stool examinations were executed one whole year and two whole years after the initial examination. both by flotation technic and by culture.each repeated twice at short intervals. At each examination.3 specimens were taken for flotation and 2 specimens for culture per capita. The examination conducted in the second year or one year after the initial examination revealed 16.5% spontaneous conversion to negative. and that of the third year 16.7% conversion among the remaining positive cases. The ratio of spontaneous conversion to negative was higher among the prisoners of shorter imprisonment; by species. it was higher for those who were infected only with Anchylostoma duodenale; and by degree of infection. it was higher for those of mild infection.