The improvement of Group A—uninfected children—proved to be greatest, and was taken as 100 per cent. On this basis, Group B—infected children not treated—showed the least improvement,—only 34 per cent. Group C—children completely cured of infection—improved 60 per cent. Group D—severely infected children, treated but not completely cured—improved 38 per cent, and Group Du—an older sub-group of D—improved 9 per cent as much as the normal children, and much less than the untreated younger children. Dr. Strong reaches the following conclusion:
"The figures show, then, that hookworm disease unmistakably affects mental development. Treatment alleviates this condition to some extent but it does not, immediately, at least, permit the child to gain as he would if he had not had the disease. And the figures apparently further show that prolonged infection may produce prolonged effects upon mentality,—effects from which the individual may never recover."
CHAPTER II.
METHOD AND PROCEDURE
The following investigation was carried on during the year and a half from October, 1919, to April, 1921. The subjects were pupils at Public School 64, Manhattan, or patients at the Manhattan Eye, Ear and Throat Hospital. All were boys, between the ages of six and fourteen years. The testing in the study of improvement was done by the investigator, assisted by three other examiners, all competent and experienced in the technique of giving psychological tests.
A Statistical Study
In addition to the more lengthy experiment, a statistical study was made, comparing the intelligence levels of two groups of children, the one selected for the presence of tonsils, the other for freedom from them. These two groups were obtained from a large group of 530 children whose I.Q.'s were gained from the records of Public School 64, where, so far as possible, all children are tested upon entering school. We had, therefore, a group unselected for intelligence level.
All the children for whom we had I.Q.'s were examined by the school nurse or physician. On the basis of this examination the two groups were selected. The tonsil group consisted of those cases which in the opinion of the nurse or doctor, were pronounced enough to deserve treatment. The normal group was composed of those who were not defective, or in whom the defect was so slight as not to demand treatment. The two groups were arranged each in a surface of distribution according to the I.Q.'s of the members. The results of the distribution appear in Table I, and in Figs. I. and II.