DISCOVERY 



119 



Various discrepancies have been recorded by sub- 

 sequent workers who have used this method, but I 

 have shown {Analyst, loc. cit.) that these are to be 

 attributed to the fact that "ink " is not a standard 

 reagent, but varies in its composition witliin wide 

 limits. A reagent made by dissolving pyrogallol in 

 osmium tetroxide (the osmic acid of the microscopists) 

 gives an ink which darkens immediately on paper and 

 gives very sharp results in the development of finger- 

 prints, whereas an ordinary fountain-pen ink only 

 darkens gradually on oxidation by the air. 



Good results can be obtained with either ordinary 

 ink or the pyrogaUic ink reagent after a long time, and 

 I have developed latent prints on paper after a period 

 of more than three years. 



The use of a gaseous reagent has many advantages 

 over liquid or solid reagents. Iodine vapour gives 

 good results, and I have developed prints with it after 

 several j^ears. The reagent has the drawback, how- 

 ever, of giving fugitive prints which are not easy to 

 photograph. But osmium tetroxide vapour, produced 

 by heating a little osmic acid solution in a basin, gives 

 very good permanent " positive " prints, in which 

 the ridges are grey, the furrows and the pore openings 

 on the ridge dark grey to black. The method is less 

 sensitive than development with iodine, and does not 

 develop a print after the lapse of some months In 

 the case of recent prints, however, it is very effective. 



(vol. ii, p. 257) of Dr. Locard's method of identification 

 by poroscopy, which is an extension of the finger-print 





.y/y. 



mm^-i< 



'•SI-'- 









Fig. I.— effect of a burn upon the SKIX PATTERN' OF A 



FINGER. 

 ( I) original print. (2) Immediately after bum. (3) .\fter partial recovery. 

 (4) After complete recovery. 

 {By permission of Mr. B. Wentworth.) 



and is especially useful when a good record of the pores 

 in the furrows is required. 



A good outline has already been given in Discovery 



Fi:.. ;. Fig. 3. 



Fig. 2.— FINGER-PRINT DEVELOPED .\FTER THREE YE-ARS WITH 

 ■• S\V.A.N " INK. 



Fig. 3.— FINGER-PRINT DEVELOPED AFTER THREE YE.ARS WITH 

 OSMIUM PVROGALLATE. 



system to the enumeration and classification of the 

 pores on the ridges. 



The only point in this description which requires 

 some correction is the statement (p. 259) that " Stockis 

 . . . proved experimentally that the wearing of 

 leather or indiarubber gloves need not prevent the 

 formation of finger-prints, and in February igi2, in 

 the S — • — • case. Dr. Locard put theory into practice 

 by identifying a gloved burglar without any other proof 

 than his finger-prints." 



Now, what Stockis meant was that even gloves are 

 not an absolute safeguard against the leaving of 

 recognisable imprints unless all portions of the friction 

 skin are completely protected. In Dr. Locard's case, 

 (which I have recently' read again in the original 

 French) the hand was only " gloved " in the sense that 

 it had been covered with a loosely woven " honey- 

 comb " towel — a very different thing from its being 

 in a fabric of leather or indiarubber. 



Distinctive Footprints 



Until comparatively recently the study of the patterns 

 formed by the friction ridges on the soles of the feet 

 has been almost completely neglected, and it has been 

 left to Messrs. Wilder and \\'entworth to devise an 

 efficient method of classifying the somewhat complex 

 patterns and to demonstrate their value as a means of 

 identification. Their first attempts to make use of 

 imprints from the toes were abandoned owing to the 

 fact that these areas are frequently outside the contact 

 area of a tread impression, and that even then the 

 patterns are monotonous and unsatisfactory for 



