HUMAN VERSUS NONHUMAN HAIRS
It is relatively easy to determine whether a hair is human or “nonhuman” (this term is often used instead of “animal” because, technically, humans are also animals) by a simple microscopic examination, as shown in Figure 1. Determining what kind of nonhuman hair it is, however, may be in some circumstances quite tricky because certain animals’ hairs can be similar. Animal hairs have several macroscopic characteristics that distinguish them from those of humans. First of all, animals have three types of hairs. Guard hairs are large, stiff hairs that make up the outer part of the animal’s coat. Guard hairs are the hairs that should be used for microscopic identification. Guard hairs may have a widening in the upper half of the shaft, called a shield. Below the shield, if it is present, may often be found a sub-shield stricture, a narrowing of the hair to slightly less than the normal, nonshield shaft diameter. A sub-shield stricture may be accompanied by a bend in the shaft at the stricture. Thinner, softer fur hairs fill in the rest of the coat providing warmth and bulk. Fur hairs are generic in their appearance and are typically useless for microscopic identification. The root may give an indication as to taxonomic origin, but it may also be misleading; it is best not to use fur hairs for microscopic evaluations. Finally, animals have vibrissa, the technical term for whiskers, the short to long, stiff, often white hairs around the snout and muzzle. No comprehensive study has been made on the identification of taxonomic origin by vibrissa, probably because these hairs have a long-life cycle and are lost comparatively less often than the myriad guard and fur hairs of a typical animal. Some nonhuman hairs are color banded, showing abrupt color transitions along the shaft of the hair, including the tip. Raccoons, for example, have four color bands in their guard hairs; incidentally, they are the only animals known to have this many bands. As noted earlier, scale patterns also may be useful in identifying animal hairs. The best ways to visualize scale patterns are with a scanning electron microscope or by making a scale cast and viewing it with a light microscope. The simplest method of making a scale cast is to brush clear nail polish onto a glass microscope slide and lay the hair in the still-wet polish. Before the polish dries completely, the hair should be gently “peeled” from the polish; a cast of the exterior of the hair remains in the polish. This cast can then be examined on a light microscope.
FIGURE 1 It is relatively easy to determine whether a hair is human or nonhuman by a simple microscopic examination. Animals have several macroscopic characteristics that distinguish their hairs from those of humans.
