FOR MICROSCOPICAL EXAMINATION. 121 



All fossil bone that I have tried requires Canada balsam; indeed, 

 some of it is so very friable that it requires to be treated according 

 to Mr. Newton's process, described in the " Naturalists' Circular" 

 for September, which consists in soaking the specimen in Canada 

 balsam, largely thinned by chloroform, before it is roughly cut in 

 pieces preparatory to grinding down. Some specimens of 

 Ichthyosaurus must be treated thus, whilst Pterodactyle is brittle 

 and transparent, so that this method would obliterate the very 

 delicate canaliculi. The finest example of fossil bone which I 

 possess was the result of an experiment on a specimen of Coccos- 

 teus obloncnis, an old red sandstone fish from Caithness. In 

 examining a specimen split from one of those water-worn pebbles, 

 which frequently form the bed of a mountain torrent in the High- 

 lands, I detached a fragment with a knife's point, about the size 

 of a pin's head. This I soaked in turpentine and mounted in fluid 

 balsam ; this rendered the fragment somewhat transparent at the 

 edges, and I saw the lacunee and canaliculi completely injected with 

 a fine red material, rendering the finest of them beautifully defined. 



The scales of Lepidotus from the Wealden are soft and opaque, 

 and require great care, but show lacunje exactly resembling those 

 of the living Lepidosteus. The bone of Dinornis differs in nothing 

 from recent bone, excepting the loss of the animal matter. 



Another form in which calcareous matter is found to exist in 

 the animal body, is in the organs known as teeth. Here, in all 

 mammalian animals, it exists under three conditions, viz., enamel, 

 dentine, and cement. 



A section of human tooth mounted in the ordinary way in 

 Canada balsam, under a moderate power, shows these materials 

 easily enough. The cement, — partaking, more or less of the cha- 

 racter of bone ; — the dentine, or ivory, as fine, undulating tubes ; — 

 the enamel also in parallel tubes, but evidently of a much denser 

 and firmer texture. 



Under a high power the enamel is seen to consist of hexagonal 

 prisms, packed closely together. The dentine is seen as tubes run- 

 ning through a matrix ; the matrix itself, under the highest powers, 

 is stnictureless. Upon the table is the tooth of the horse and one 

 of the elephant, and the jaws, with the teeth entire, of a Cestracion, 

 or Port Jackson shark. 



The two former show distinctly, even as hand specimens viewed 

 with a lens, the three component materials — enamel, dentine, and 



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