STRUCTURE OF WHALEBONE. BLOOD-CORPUSCLES. 700 



Transverse section of Horn of Rhinoceros, viewed 

 by Polarized Light. 



shadows of this cross are replaced by contrasted colours, when the 

 Selenite plate is 



interposed. The Fig. 369. 



substance com- 

 monly but erro- 

 neously termed 

 Whalebone, which 

 is formed from the 

 surface of the 

 membrane that 

 lines the mouth 

 of the Whale, and 

 has no relation to 

 its true bony skele- 

 ton, is almost iden- 

 tical in structure 

 with Rhinoceros 

 horn, and is simi- 

 larly affected by 

 Polarized light. 

 The central por- 

 tion of each of its 

 component fibres, 

 like the Medullary 

 substance of Hairs, contains cells that have been so little altered as 

 to be easily recognized ; and the outer or Cortical portion also may 

 be shown to have a like structure, by macerating it in a solution 

 of potass, and then in water. — Sections of any of the Horny tissues 

 are best mounted in Canada balsam. 



555. Blood. — Carrying our Microscopic survey, now, to the 

 elementary parts of which those softer Tissues are made up, that 

 are subservient to the active life of the body rather than to its 

 merely-mechanical requirements, we shall in the first place notice 

 the isolated floating cells contained in the Blood, and known as 

 the Blood-Corpuscles. These are of two kinds ; the 'red,' and 

 the ' white ' or ' colourless.' The Red present, in every instance, 

 the form of a flattened disk, which is circular in Man and 

 most Mammalia (Fig. 371), but is oval in Birds, Reptiles 

 (Fig. 370), and Fishes, as also in a few Mammals (all belonging to 

 the Camel tribe). In the one form, as in the other, these Cor- 

 puscles seem to be flattened cells, the walls of which, however, are 

 not distinctly differentiated from the viscid substance they con- 

 tain ; as appears from the changes of form which (as shown by 

 Dr. Beale) they spontaneously undergo when kept at a temperature 

 of about 100°, and from the effects of pressure in breaking them 

 up. The Red corpuscles in the blood of Oviparous Yertebrata are 

 distinguished by the presence of a central spot or Nucleus, 

 which appears to be composed of an aggregation of minute 



