So far we have considered the causes of mental deficiency of hereditary origin. The causes in general may be grouped roughly under direct, which are due to heredity or disease, and indirect, due to sense defects and accidents. About 85 per cent, of the cases may be traced to conditions prior to birth, such as bad heredity, neurotic conditions, alcoholism and tuberculosis. Injuries at birth are at the present time rare and are responsible for not over 1 per cent., according to the best authoritories. The remainder may probably be counted for by accidents, infectious diseases, epilepsy, malnutrition, etc., after birth.
Fig. 5. Placing Blocks in the Form Board. With this form board, another type of test used in America, the child is required to place the ten blocks as rapidly as possible in their respective places. The experimenter observes and notes superfluous and jerky movements, the adoption of a method or system, i. e., hunting the block to fit the space and vice versa, the ability to profit by experience when the test is repeated, the ability to increase a set pace of procedure, the degree of sustained attention, the span of motor control, and many other phases of mental expression. One bright boy of ten recently placed the blocks in their respective places in twelve seconds and a defective of nineteen required, after much urging and many vacillating and uncoordinated movements, seven minutes and eighteen seconds. Dr. Healy, psychopathologist for the Chicago Juvenile Court, has modified this type of form board by having the geometric forms a part of a puzzle picture which covers the face of the board.
This test alone throws much light on the mind of a child and may be used as a diagnostic test for children of varying grades of arrested mental ability.
Fig. 6. A Test for Reflex Action and Motor Control. The apparatus as shown consists of a piece of glass in a frame which is struck by a rubber hammer. Low-grade defectives seldom wink.
