Examine carefully a ridge which has been printed--and, if possible, photographically enlarged--at various periods not long apart, and the pores with which it is dotted will be found, while retaining their relative positions, to vary somewhat in their degree of patency. A single ridge might be compared to a naval cruiser, the numerous funnels of which are not all belching forth smoke at the same time, but one is almost smokeless while its neighbour is quite active. Those pores which have been copiously emitting sweat are seen, when imprinted, to be larger than those that were inactive. An imaginary case was once suggested to me as a final blow to finger-print identification. A certain Mr. William Sykes is officially known to be recruiting his valuable health at one of His Majesty’s sanatoriums for people of his profession. That celebrated artist’s “thumb”-print, however, has been found liberally spotted all over the scene of some tragic area of crime. What is to be said? Well, the prodigality of display of the well-known sign-manual, in circumstances when gloves are almost invariably now worn by experts, might well arouse suspicion in itself, but it would easily be found in such a case that the pattern had been prodigally repeated with too great fidelity in the matter of sweat-pores, which, in the case of an active burglar, who is a sober, hard-working fellow in spite of his faults, would vary with each successive imprint, in a way that no manufacturer of bogus “thumb”-prints could easily follow. The fact that a finger--a clean finger--is naturally, to some slight extent, greasy, partly from sebaceous secretion, enables the expert dactylographer by various chemical and mechanical means to obtain a pretty clear vision, even in minute detail, of what before had been quite invisible. A mere accidental smudge from a slightly oily palm or finger, if imprinted on glass, japanned tin, varnished or polished wood, etc., may have its invisible lineations brought out by dusting gently upon it some light powder of appropriate colour. Dr. René Forgeot, in 1891, first called attention to this method of bringing out latent imprints, and my friend, Dr. Garson, of this country, gave it further developments. In my _Guide_ I have mentioned some of my own results with modifications of these methods.