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The popular idea was that a human hair was a hollow cylinder, 

 that its colour was owing to the presence of a fluid within the 

 cylinder, and that it grew with roots much in the same way as a 

 tree. That a hair originated in a bulbous root contained in a 

 depression in the skin was very certain, but there the analogy 

 between it and a tree ended. A tree increased by a prolongation of 

 its stem, through an addition to its cells from the apex, whereas a 

 hair lengthened by an addition of cells to the basal portion, which 

 pushed the rest of the hair forward. 



Carefully examined under the microscope, a human hair 

 consisted of three parts, the cuticle, the cortical substance, and the 

 medullary substance. The cuticle consisted of epithelial cells, lying 

 over each other like tiles, from one end of the hair to the other. 

 The ends of the scales stood out from the surface and gave its 

 outer circumference a jagged appearance. These scales caused the 

 hair to appear as if there were fine irregular lines crossing its 

 surface. These scales were a very important part in the economy 

 of some hairs, because they accounted for the ease with which the 

 wool or hair of some animals felted. The cortical substance, which 

 formed the pi-incipal, and in some cases the whole, of the shaft, 

 consisted of closely packed cells in rows, and lying neai'ly parallel 

 to the axis of the hair, thus giving to some hairs the appearance as 

 if striped lengthwise. These cells were so closely united that only 

 under the action of concentrated sulphuric acid could they be 

 separated into spindle-shaped cells. 



It was in the cortical substance that the colouring matter, 

 sometimes diffused through the mass, but generally scattered in 

 pigment cells, was found. The cortical substance also contained a 

 number of cavities filled with air. These were most patent in dry 

 hair, or that from the head of adults or the aged. The medullary 

 substance generally occupied the centre, when present, because in 

 woolly hair and that from a new-born child it was absent, also in 

 some examples, of blonde hair. Some considered the meduUai-y 

 substance cellular, others thought it was not, but the general 

 opinion inclined to the cellular. It had also been thought to 

 contain the pigment, but the supposed pigment granules were 

 minute air-bubbles. The medullary substance was best made out 

 in white hair. 



