136 



ELEMENTS OF APPLIED MICROSCOPY. 



of the ridges and furrows characteristic of that digit, a 

 record necessarily free from the error which may attend 

 ordinary anthropometric measurements. GaUon has 

 shown that the pattern of the skin persists unchanged 

 through life and is unaltered in its essentials by cuts, 

 burns, or any ordinary accidents. The variations are so, 

 great that he calculated the chances of identity between 

 two single prints to be only one in sixty-four billion. 

 When ten digits are compared, identification is absolute. 



Such records, in order to be of any practical service, 

 must be readily arranged and classified; this Galton 



1 2 ' 



Fig. 51. — F1NGEE.-PKINT Patterns. (Redrawn after Galton.) 

 has done so successfully that, out of a "finger-print direc- 

 tory" of 2632 persons, any pattern could be located in 

 three minutes. In the first place, the patterns of the skin 

 may be grouped under three heads. In all cases the 

 papillary ridges run across the fingers in the vicinity 

 of the third joint, and at the tip they follow the curve 

 of the nail in a rounded arch. Sometimes the ridges 

 between follow the outer ones in a more or less even 

 arch of lessening convexity; this is the arch type (i. Fig. 51). 

 Sometimes the intermediate ridges form a loop running 

 from one side inward to the center of the bulb and then 

 doubling back again. Obviously at the opposite side 



