Student Question

Calculate the medullary index of a hair whose diameter is 110 microns wide and whose medulla measures 58 microns. Is this a human or animal hair? 

Expert Answers

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Each strand of hair has some layers, with medulla be the innermost. It is a hollow tube inside a hair, and its role is unknown yet. It may be present or absent, and if it is present, it may be continuous or fragmented. The presence of medulla and its character differs from person to person and from one strand to another within the same person.

The medullary index is defined as the ratio between the diameter of medulla and the diameter of the entire hair,

medullary index = (medulla diameter) / (hair diameter)

(this is a dimensionless unit).

It is known that a human's medulla is considerably thinner than an other animal's one. For animals, it is 1/2 or more, for humans, 1/3 or less.

At the given case, the index is `58/110 approx 0.53 gt 1/2 = 0.5.` So this is an animal hair.

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