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X.]   DISEASE.   167

bide their time ; they are insufficient for the period in question. By attempting to work with incompleted life histories the risk of serious error is incurred.

Data.-The Schedule in Appendix G, which is illustrated_ in more detail by Tables A and B that follow it, shows the amount of information that I had hoped to obtain from those who were in a position to furnish complete returns. It relates to the "Subject" of the pedigree and to each of his 14 direct ancestors, up to the great-grandparents inclusive, making in all 15 persons. Also, to the Fraternities of which each of these 15 persons was a member. Reckoning the total average number of persons in each fraternity at 5, which is under the mark for my R.F.F collection, questions were thus asked concerning an average of 75 different persons in each family. The total number of the Records that I am able to use, is about 160; so the aggregate of the returns of disease ought to have been about twelve thousand, and should have included the causes of death of perhaps 6,000 of them. As a matter of fact, I have only about one-third bf the latter number.

Trustworthiness of R. F. F.. data. The first object was to ascertain the trustworthiness of the medical information sent to me. There is usually much disinclination among families to allude to 'the serious diseases that they fear to inherit, and it was necessary to learn whether this tendency towards suppression notably vitiated the returns. The test applied was both simple and just.