Of laboratory tests many have been devised. While all yet leave much to be desired, still through their application the majority of mental defectives can be detected. Fairly accurate standards of normality have been established from which the relative degree of "backwardness" can be determined. We have just awakened to the importance of detecting defectives early in life, hence many of our tests have been planned with reference to children. They are based not so much on training or conscious learning as on fundamental processes which develop at certain ages in children. Another impetus toward securing adequate criteria of mental deficiency has been the crying need of having some easily applied standard for detecting the very large numbers of defective immigrants who are continually seeking to enter the United States. Most of the methods consist of "performance" tests which are planned to test the powers of perception, concentration, application, ingenuity and education of the subject. Previous environment, education and the difficulties under which the subject may be laboring at the time of the test must, of course, be taken into account. It is particularly difficult to get adequate tests for the immigrant which will enable one to distinguish between ignorance, stupidity, fear and temporary psychic depression on the one hand, and congenital mental deficiency on the other. Perhaps the most successful single set of tests for mental deficiency is that known as the Binet-Simon Scale. From an examination of large numbers of French school children Binet constructed a scale of tests of increasing complexity accurately graded to age and previous training of the average normal child. In the Binet-Simon system tests are given for each age from three years to thirteen. When a child successfully passes the tests for his age he is classed as normal. If he succeeds only in tests which normally are those given for a child a year younger then he is backward to the extent of one year. Similarly he may show by these graded tests that he is backward to the extent of two years, three years and so on. If a child is more than three years backward according to the test he is regarded as mentally defective. Various corrections and adjustments of the original scale have been worked out to allow for unevenness in mental development. On the whole the scheme works out satisfactorily when applied by one skilled in its use. The attitude of the examiner, however, is of so great importance that the tests are of less value in the hand of inexperienced workers. A revision of the scale to adapt it better to American children has recently been made by Doctor Goddard.[10] Besides the Binet-Simon tests various performance tests, standardized for children of different ages, such as Seguin's form board, Healy's pictorial completion test, Fernald's construction puzzle, the Rossolimo test, De Sanctis test, etc., are used by different investigators. Questions