Medullary Index
Definition
The ratio of the medulla diameter to the total hair shaft diameter. In companion animal hair identification, a medullary index above 0.5 is typical of many domestic animals (compared to below 0.3 in most human hairs), and the medullary pattern (continuous, interrupted, fragmented) varies by species and assists microscopic species identification.
- Human hair range
- Typically less than 0.33, often absent
- Animal hair range
- Usually greater than 0.50
- Use in microscopy
- Preliminary screening criterion in hair comparison microscopy
Common questions
How is medullary index measured in hair analysis?+
The medullary index is the ratio of the medulla diameter (the innermost core) to the total hair shaft diameter. It is measured at the widest point in a cross-section or cleared preparation of the hair under a microscope.
Why is medullary index useful in forensic hair identification?+
It serves as a preliminary screening tool to distinguish human hair from animal hair. Human hair typically has a medullary index below 0.33, while most animal hairs are above 0.5. This quick calculation helps narrow down the source when DNA cannot be recovered from the shaft.
Can medullary index alone identify a specific animal species?+
No. While different wildlife species have characteristic medullary index ranges, the index alone is not sufficient for reliable species-specific identification. Additional microscopic features of the hair shaft are needed to confirm species.
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Explained in these topics
- Big Cat and Bear Product IdentificationThe ratio of medulla diameter to total hair shaft diameter, measured in cross-section or cleared preparation. Species-specific ranges allow hair identification...
- Companion Animal and Veterinary Forensic BiologyThe ratio of the medulla diameter to the total hair shaft diameter. In companion animal hair identification, a medullary index above 0.5 is typical of many dom...
- Hair and Fibers: Nature, Types, Structure and ExaminationRatio of medulla diameter to total hair diameter. Human hair typically less than 0.33 (often absent); animal hair greater than 0.50. A single-number favourite.
- Hair Examination and MicroscopyThe ratio of medulla diameter to total hair shaft diameter, measured at the widest point. Values below 0.33 are characteristic of human hair; values above 0.50...
- Hair, Feather, and Surface Covering IdentificationThe ratio of medulla width to total hair shaft width, measured at the widest point in a transverse mount. Values above 0.5 are common in wildlife species; huma...
- Stereo Microscope and Comparison MicroscopeThe ratio of medulla diameter to total hair shaft diameter; human hair typically less than 0.33, most animal hairs above 0.5. A preliminary screening criterion...