 In this lesson, you will learn the basics of visual identification of hair and fiber evidence. We're going to be talking about the different shapes and patterns of hairs and fibers, and how to analyze these microscopically. I'm going to be showing you some examples of microscopic images using a ProScope HR digital microscope, which links the images directly to my computer screen. This piece of equipment is commonly used by forensic scientists. Let's begin by discussing some basic visual differences between hairs and fibers. Fibers can be uniform or irregular in shape, depending on the type of fiber. Synthetic fibers are very uniform in shape, while natural fibers are irregular. By contrast, hairs are always going to be irregular in shape, since they are natural and have unique cell structures. Fibers can take a variety of shapes, and we'll talk about some of the most common ones. Hairs, however, only take one shape, circular. Also, hairs have some very recognizable structural features, the cuticle and the medulla, and we'll talk later about how to identify those. Fibers do not contain these features, so the absence of a cuticle and medulla can be informative for evidence identification. I want to briefly explain what kinds of information can be gathered from hair and fiber evidence. With fibers, you can determine whether it is a natural or man-made fiber. Man-made fibers are commonly called synthetic. Forensic scientists can compare a question fiber with a potential source to determine if the fiber is consistent with that source. Fibers are always class evidence, meaning they cannot be identified to a specific source. With hair evidence, the first thing a forensic scientist will determine is whether or not the hair is human. If it is not human, the hair's cuticle pattern can be used to identify the species. If the hair does belong to a human, you can assess ancestry, where the hair came from on the body, the length of the person's hair, and whether or not it was treated with hair dye. If the root of the hair is present, you can determine if the hair was naturally shed or forcibly removed, and you can also perform a DNA analysis to make an identification. But the things we'll be talking about today relate only to what you can determine from a basic microscopic analysis. Things like natural versus synthetic fiber, human versus non-human hair, and species identification. Let's start with hair. I want to begin by explaining some of the major ways to distinguish hairs and fibers using microscopic analysis. Hairs have distinct structural features that make them very visually distinct from fibers. When you look at a hair under a microscope, you will immediately see the cuticle and the medulla, which would not be present on a plant fiber or synthetic fiber. This image shows you the basic structure of a hair. The two main components of hair that we'll talk about today are the cuticle and medulla. The cuticle is the outer layer of hair that's composed of overlapping scales. These scales form different patterns in different species, which is great for human versus non-human determinations. There are three main cuticle patterns, coronal, spinus, and imprecate. Coronal cuticle patterns look like stacked paper cups, and they are common in small rodents and bats. Spinus cuticle patterns look like flower petals. This pattern is visible in cats, among other species. This is a cat hair under the ProScope digital microscope that I showed you earlier. I want to draw your eye to the cuticle pattern along the outer layer of the hair, which you can see here. If you put this hair under a high-powered, scanning electron microscope, the spinus cuticle pattern is clearly visible. Third major cuticle pattern is called imprecate, and it's composed of narrow scales that look a little bit like stacked bricks. Humans and dogs have this cuticle pattern. This is a dog hair magnified using the ProScope microscope. Hopefully you can see the scales of the cuticle in this picture. I've outlined them for you here. If you magnified the dog hair using a scanning electron microscope, the imprecate pattern would be much clearer. This is a human hair under the ProScope microscope. You can just make out the cuticle pattern here. If you put the human hair under a scanning electron microscope, the imprecate pattern comes out very clearly. One other major structural feature visible in hairs is the medulla. This is a canal-like structure that runs through the center of hairs. The medulla can take different patterns and thicknesses, and it can even be absent altogether. This is never present in plant fibers and synthetic fibers, so if you do see a medulla, you immediately know it's a hair. The diameter of the medulla can be used for human versus non-human determinations. This measurement is called the medullary index, and is the ratio of medulla thickness to overall hair thickness. You can see here that humans tend to have a thinner medulla, and animals tend to have a thicker medulla. This is a cat hair under the ProScope. Note the thick medulla in relation to overall hair thickness. This is an image of a dog hair using the ProScope. Again, note the thick medulla in comparison with overall hair diameter. Here we have a human hair, magnified with the ProScope. In this hair, the medulla is slightly thinner when compared to the overall thickness of the hair. So, in summary, hairs can be easily distinguished by the presence of a cuticle and medulla, and these features are helpful in human versus non-human determinations along with species identification. Now let's move on to the microscopic analysis of fibers. I mentioned previously that there are two general categories of fibers, natural and synthetic. Natural fibers include animal hairs, vegetable fibers, meaning fibers that come from plants, and mineral fibers like asbestos. Synthetics include organic fibers such as polymers, like polyester, and inorganic fibers such as fiberglass. Again, natural fibers consist of fibers from animals and plants. These tend to be irregular in shape. As you've seen, animal hairs are circular, but they have irregular cuticle patterns. Plant fibers, also called vegetable fibers, are highly irregular in shape. So, when I say irregular, I mean that each fiber will look a little bit different. Plant fibers also tend to be twisted. Here is an image of a cat hair using the ProScope digital microscope. Under the microscope, you can tell that the hair is circular with an irregular outer surface, the cuticle. This is an image of cotton under the ProScope. Cotton is a type of plant, so this would be a vegetable fiber. Cotton is flat, ribbon-like, and twisted, and as you can see here, it has a very unique irregular shape. Synthetic fibers take a variety of shapes, but within those shapes, the fibers are all very uniform, meaning their characteristics are very consistent between samples. They don't contain the imperfections and unique shapes that natural fibers do. The most common shapes for synthetic fibers are trilobal, hollow, and circular. This is what trilobal synthetic fibers look like under a high-powered scanning electron microscope. These are hollow synthetic fibers under a scanning electron microscope. And here you have circular synthetic fibers under a scanning electron microscope. Notice how perfectly circular and uniform these fibers are. Even though animal hairs are circular, by the end of this lesson, you should be able to tell the difference between circular animal hairs and circular synthetic fibers based on the presence or absence of a cuticle pattern and whether it has an irregular or uniform shape. Here you have an image under the proscope digital microscope. This is polyester, a synthetic fiber. Notice how perfectly circular these fibers are. This is another microscopic image under the proscope, but this fiber is acrylic, again a synthetic fiber. Acrylic actually has a different shape than the three main shapes we previously discussed. Acrylic in cross-section has a dog bone shape due to a depression running along the length of the fiber. You can see that depression in the image here. From these images, you should be able to get a sense of the wide variety of fiber shapes. So through this lesson, you have learned that hairs and fibers can be easily identified and distinguished by their shape, structural features, and degree of uniformity or irregularity.