ERRORS OF INTERPRETATION. 67 



Another very characteristic fallacy resulting from con- 

 figuration is furnished in the supposed tubular structure 

 of human hair. When we view this object by transmitted 

 light, it presents the appearance of a darkish flattened 

 band down the centre ; this, however, is entirely due to 

 the convergence of the rays of light produced by the 

 convexity of the surface of the hair. That it is a solid 

 structure is proved by making a transverse section of the 

 hair-shaft, when it is seen filled up with medullary sub- 

 stance, with the centre somewhat darker than the other 

 part. It is, in fact, a spiral outgrowth of epithelial scales, 

 overlapping each other like tiles on a house-top, and this 

 gives a striated appearance to the surface. A cylindrical 

 thread of glass in balsam appears as a flattened, band-like 

 streak, of little brilliancy. Another instance of fallacy 

 arising from diversity in the refractive power of the in- 

 ternal parts of an object, is furnished by the mistakes for- 

 merly made with regard to the true character of the lacunae 

 and canaliculi of bone-structure, which were long mis- 

 taken for solid corpuscles, with radiating opaque filaments 

 proceeding from a dense centre ; we now know them to 

 be minute chambers, with diverging passages, excavated in 

 the solid osseous substance. That such is truly the case, 

 is shown by the effects of Canada balsam : as this infil- 

 trates the osseous substance, and fills up the excavations, 

 it quite obliterates the bone corpuscles. 



The molecular movements of finely divided particles, 

 seen in nearly all cases when certain objects are first 

 suspended m water, or other fluids, is often a source of 

 embarrassment to beginners. If a minute portion of 

 indigo or carmine be rubbed up with a little water, and 

  a drop placed on a glass slide under the microscope, it will 

 at once exhibit this peculiar perpetual motion appearance. 

 This movement was first observed in the granular particles 

 seen among the pollen grains of plants, known as fovilla, 

 which are set free when the pollen is crushed. Important 

 vital endowments were formerly attributed to these par- 

 ticles, but Dr. Eobert Brown showed such granules were 

 common enough both in organic and inorganic substances, 

 and therefore they were in no way particularly "indicative 

 of life." We must especially notice another point which 



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