Bearing in mind that mediocrities differ less from one another than members of either of the extreme classes, and would therefore be more difficult to distinguish, it seems probable that with comparatively few exceptions, _at least_ two thousand adults of the same sex might be individualised, merely by means of twelve careful measures, on the Bertillon system, making reasonable allowances for that small change of proportions that occurs after the lapse of a few years, and for inaccuracies of measurement. This estimate may be far below the truth, but more cannot, I think, be safely inferred from the above very limited experiment.
The system of registration adopted in the American army for tracing suspected deserters, was described in a memoir contributed to the "International Congress of Demography," held in London in 1891. The memoir has so far been only published in the _Abstracts of Papers_, p. 233 (Eyre and Spottiswoode). Its phraseology is unfortunately so curt as sometimes to be difficult to understand; it runs as follows:--
Personal identity as determined by scars and other body marks by Colonel Charles R. Greenleaf and Major Charles Smart, Medical Department, U.S. Army.
Desertions from United States army believed to greatly exceed deserters, owing to repeaters.
Detection of repeaters possible if all body marks of all recruits recorded, all deserters noted, and all recruits compared with previous deserters.
In like manner men discharged for cause excluded from re-entry.
Bertillon's anthropometric method insufficient before courts-martial, because possible inaccuracies in measurement, and because of allowable errors.
But identity acknowledged following coincident indelible marks, when height, age, and hair fairly correspond.
That is, Bertillon's collateral evidence is practically primary evidence for such purposes.
There is used for each man an outline figure card giving anterior and posterior surfaces, divided by dotted lines into regions.
These, showing each permanent mark, are filed alphabetically at the Surgeon-General's office, War Department.
As a man goes out for cause, or deserts, his card is placed in a separate file.
The cards of recruits are compared with the last-mentioned file.