Sweat secreted by the eccrine glands on the fingertips is deposited on surfaces the fingers touch. The deposition in the form of contours, which are the mirror images of the ridge patterns on the fingers. The patterns formed by fingerprints fall into three well-defined categories: arches, loops, and whorls (Figure 1, Student Side). The constituents of sweat may be selectively fixed by different chemical reagents so as to make latent (invisible) fingerprints visible.
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