SOLID PARTS OF ANIMALS. 



The scales of fish, as had been observed by Lewenhoeck, are 

 composed of different membranous lamina?. When immersed 

 for four or five hours in nitric acid, they become transparent and 

 perfectly membranaceous. The acid, when saturated with am- 

 monia, gives a copious precipitate of phosphate of lime.* Hence 

 they are composed of alternate layers of membrane and phos- 

 phate of lime. To this structure they owe their brilliancy. Mr 

 Hatchett found the spicula of the shark's skin to be similar in its 

 composition, but the skin itself yielded no phosphate of lime. 



The horny scales of serpents, on the other hand, are compos- 

 ed alone of a horny membrane, and are destitute of phosphate of 

 lime. They yield, when boiled, but slight traces of gelatin ; the 

 horn-like crusts which cover certain insects and other animals 

 appear, from Mr Hatchett's experiments, to be nearly similar in 

 their composition and nature. 



Thus it appears that these substances bear a striking resem- 

 blance to each other, being composed of a membrane which 

 Hatchett considers as coagulated albumen. Vauquelin, however, 

 who affirms that they dissolve in water, provided the temperature 

 be raised sufficiently in a digester above the boiling point, consi- 

 ders them, on that account, rather as a species of concrete mucus 

 than as coagulated albumen, f 



CHAPTER XVIII. 



OF HARTSHORN. 



THE horns of the buck and hart, and indeed of the whole 

 tribe of deer, are quite different from those which have been 

 treated of in the last chapter. They are branched, and possess 

 the hardness of bone. From the experiments of Scheele and 

 Rouelle, together with those of Hatchett, we know that these 

 substances possess exactly the properties of bone, and are com- 

 posed of the same constituents, excepting only that the propor- 

 tion of cartilage is greater. They are intermediate, then, be- 

 tween bone and horn. The same remarks apply to a fossil horn 



* Hatchett, Phil. Trans, 1799, p. 332. f Nicholson's Jour. xv. 147. 



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