THAT HAIRS ARE TUBES 203 



false and the life history of the Gordius has been fully 

 traced. 



It may interest some of our younger readers to learn 

 that these worms get the name Gordius because of their 

 curious habit of coiling themselves into complicated knots 

 veritable " Gordian knots." 



THAT HAIRS ARE TUBES 



we look through a strong magnifying glass 

 a human hair it appears to the uneducated 

 eye to be tubular and consequently the impres- 

 sion very generally prevails that hairs, like quills, 

 are tubes. This fallacy is due to the fact that since the 

 hair is nearly cylindrical there is generally a bright line 

 of light reflected from the upper part of the surface, and 

 as the edges are in shade and consequently dark, the re- 

 semblance to a tube is very strong. But if we place a 

 bright metallic wire under a microscope and examine it 

 as a dry and opaque object, the same bright central line 

 and dark edges will appear and the wire will seem to be a 

 tube, although we know that such is not the case. Of 

 course the decisive test is to make a cross section of the 

 hair and examine this under the microscope after it has 

 been properly mounted. The interior substance of the 

 hair will then be found to consist of a peculiar fibrous ma- 

 terial with sometimes a central medullary portion composed 

 of spheroidal cells. 



The hairs of different mammals vary greatly in their 

 structure. Those of the cat, squirrel, mouse, rabbit, and 



