of the Texas School Book Depository following the assassination, Commission Exhibit No. 142; (3) the shirt worn by Oswald on November 22, 1963, Commission Exhibit No. 150; and (4) the C2766 rifle, Commission Exhibit No. 139.

General Principles

Hairs.--As shown in Commission Exhibit No. 666 (p. 587), a hair consists of a central shaft of air cells, known as the medulla; a cortex containing pigment granules (which give the hair its color) and cortical fusi (air spaces); and a cuticle and an outer layer of scales. Unlike fingerprints, hairs are not unique. However, human hairs can be distinguished from animal hairs by various characteristics, including color, texture, length, medullary structure and shape, shape of pigment, root size, and scale size. In addition, hairs of the Caucasian, Negroid, and Mongoloid human races can be distinguished from each other by color, texture., size and degree of fluctuation of diameter, thickness of cuticle, shape and distribution of pigment, and shape of cross-section. Moreover, even though individual hairs are not unique, the expert usually can distinguish the hairs of different individuals. Thus, Stombaugh, who had made approximately 1,000 comparison examinations of Caucasian hairs and 500 comparison examinations of Negroid hairs, had never found a case in which he was unable to differentiate the hairs of two different Caucasian individuals, and had found only several cases in which he could not distinguish, with absolute certainty, between the hairs of two different Negroid individuals. 344

Fibers.--Like hairs, the various types of natural and artificial fibers can be distinguished from each other under the microscope. Like hairs too, individual fibers are not unique, but the expert usually can distinguish fibers from different fabrics. A major identifying characteristic of most fibers is color, and under the microscope many different shades of each color can be differentiated--for example, 50-100 shades of green or blue, and 25-30 shades of black. The microscopic appearance of three types of fibers---cotton, wool, and viscose-is illustrated in Commission Exhibit No. 665 (p. 589). Two of these, cotton and viscose, were the subject of testimony by Stombaugh. Cotton is a natural fiber. Under the microscope, it resembles a twisted soda straw, and the degree of twist is an additional identifying characteristic of cotton. Cotton may be mercerized or (more commonly) unmercerized. Viscose is an artificial fiber. A delustering agent is usually added to viscose to cut down its luster, and under the microscope this agent appears as millions of tiny spots on the outside of the fiber. The major identifying characteristics of viscose, apart from color, are diameter--hundreds of variations being possible -- and size and distribution of delustering agent, if any. 345

The blanket.--Stombaugh received the blanket, Commission Exhibit No. 140, in the FBI Laboratory at 7:30 a.m., on November 23, 1963.346 Examination showed that it was composed of brown and green fibers, of which approximately 1-2 percent were woolen, 20-35 percent