OF THE ANIMAL FRAME. 



tU 



Lime, however, is never found in the animal system in its pure state^^ 

 and is certainly never introduced into it in such a state. It is usually com- 

 bined with some acid, either the phosphoric, in which case the compound 

 is called phosphate of lime, or carbonic acid gas, when it is called car- 

 bonate of lime, or common chalk. 



It is of no small importance to attend to the nature of these two acids ; 

 for it is the difference between them that chiefly constitutes the difference 

 between bones and shells ; bones uniformly consisting of a larger propor*- 

 tion of phosphate of lime, or lime and phosphoric acid, and a less propor- 

 tion of carbonate ; and shells of a larger proportion of carbonate of lime, 

 and a less proportion of phosphate. There are a few other ingredients 

 that enter into the composition of both these substances, and which are 

 chiefly obtained from the materials of common salt, as sulphuric acid and 

 soda ; but the proportions are too small to render it necessary to dwell 

 upon thern in a course of popular study. Bones, shells, cartilages, and 

 membranes may therefore be regarded as substances of the same kind, 

 differing only in degree of solidity from the different proportions that they 

 possess of albumen and salts of lime. 



Teeth, horn, coral, tortoise-shell, fish-scales, and the crustaceous in- 

 teguments of crabs, millepedes, and beetles, are all compounds of the 

 same elements combined in different proportions, and rendered harder or 

 softer as they possess a larger or smaller quantity of calcareous salts ; ivory 

 and the enamel of teeth possessing the largest quantity, and consisting 

 almost exclusively of phosphate of lime, with a small proportion of animaf 

 matter. 



The gelatine and albumen are unquestionably generated in the animal 

 system itself from the different substances it receives under the form of 

 food ; and it is curious to observe the facility and rapidity with which 

 some animals are capable of producing them. The gastrobranchus Ccecus^ 

 or hag-fish, a small lamprey-like animal of not more than eight inches long, 

 will convert a large vessel of water in a short period of time into size or 

 mucilage, of such a thickness that it may be drawn out in threads. The 

 form and habits of this little animal are singular : Linneus regarded it as a 

 Worm ; but Bloch has removed it, and with apparent propriety, into the class 

 of fishes. It is a cunning attendant upon the, hooks of the fisherman ; 

 and as soon as it perceives a larger fish to be taken, and by its captivity ^ 

 rendered incapable of resistance, it darts into its mouth, preys voraciously, 

 like the fabled vultures of Prometheus, on its inside, and works its way 

 out through the fish's skin. 



But though gelatine and albumen are unquestionably animal produc- 

 tions, the one a secretion from the blood, and the other a constituent prin- 

 ciple of it, there is a doubt whether lime ought ever to be regarded in the 

 same character. A very large portion is perpetually introduced into the 

 stomach from without. In our lectur© on the analogy between the siruc- 

 ture of plants and of animals,* I had occasion to observe, that it forms an 

 ingredient in common salt ; not, indeed, necessarily so, but from the difli= 

 culty of separating the other ingredients from their combination with it: 

 yet it enters not more freely into common salt than into almost every other 

 article, whether animal, vegetable, or mineral, of which our diet is usiially 

 composed. And upon this common fact it is more generally conceivedo 



