82 A HALF-HOUR WITH THE 



not so strong as linen or silk, its irregular surfaces 

 permit its being spun into a strong yarn, from 

 which all cotton fabrics are made. The young 

 microscopist should make himself acquainted with 

 the forms of these various fibres ; as, from their 

 being so constantly present in rooms where the 

 Microscope is used, and occasionally employed in 

 cleaning the apparatus, they often present them- 

 selves as foreign substances, among other objects 

 that are being examined. 



It is also interesting, and sometimes of import- 

 ance, to be able to ascertain of what material a 

 fabric may be composed. Thus by means of the 

 Microscope, and that alone, we know certainly that 

 the cere-cloths in which Egyptian mummies ara 

 wrapped is a linen fabric, whilst the similar invest- 

 ment of Peruvian mummies is cotton. The hair of 

 the bat, represented at figure 186, plate 7, presents a 

 singular instance of the projection of the scales, or 

 cells, in a regular form. Hairs are not often perfectly 

 round ; in the peccary they are oval, as seen in 

 figure 187, plate 7. If a transverse section of this 

 hair is examined, it will be found that the cortical 

 substance projects completely into the pulpy part 

 of the hair in several places, so as to break up the 

 pulp into several separate sections. 



In some cases it is not easy to distinguish 

 between outside and inside structure, as seen in 

 the hair of the musk-deer, in which the whole is 

 found to consist of a mass of hexagonal cellular 

 tissue, similar to that seen in the pith of plants. 

 This hair is shown in plate 7, figure 188. 



Insects are frequently covered with hairs, espe- 

 cially in their larva, or caterpillar state. These 

 hairs when stiff and sharp, penetrate the skin, 

 and produce irritation there. This is the case with 

 the large tiger caterpillar. The hairs of this cater- 



