_The Social Isolation Group._ We are now ready to consider some of the important estimates which throw light upon the reasonableness of the percentages we have named. First, what percentage would we be justified in socially isolating? In the United States Census Report on the Insane and Feeble-Minded in Institutions in 1910, we find that the number then actually in institutions for feeble-minded was only about 0.02% of the population. At the most frequent ages this rises to about 0.05%. It is evident that the number actually isolated is of little significance except as a check on the estimates. The report, however, refers to the special estimate made by the public authorities in Massachusetts which also included feeble-minded in state hospitals for the insane, other asylums, those reported by the overseers of the poor and those enumerated in the general population. The U. S. report says: “The census was not regarded as being complete, but it is of interest to note that if the number of feeble-minded in proportion to the total population was the same for the entire United States as it was in Massachusetts according to this census, the total number of feeble-minded would be over 200,000. Probably this may be regarded as a conservative estimate of the number of feeble-minded in the United States and would indicate that not over one-tenth of the feeble-minded are being cared for in special institutions” (_205_, p. 183). This estimate, which thus amounts to about 0.2%, may probably be considered as a reasonable program of expansion from the institutional viewpoint. The diagnostician who is considering the individual and not the mass must supplement it by considering who should be isolated if facilities were available. If the census bureau can contemplate institutional care for ten times those at present thus provided for, it gives us some indication of a reasonable limit as to the increase in institutional care that can be assumed to be reasonably contemplated at present. Dr. W. D. Cornell, director of medical inspection of the Philadelphia public schools, after the personal examination of those cases which in the opinion of the teachers should be sent to institutions, places the “institution cases” at a minimum of 15 per 10,000 school children. He adds: “The number of evidently feeble-minded above 6 years of age may be said to be 1 to every 500 of the population. These figures are conservative and have been accepted by experts for years.” This then is the minimum estimate and quite clearly refers to institutional cases.