OF NATURAL HISTORY. 211 



' grow as quickly as the other organs, ia which the nerves are large 



* and numerous. 



' A year after 1 had cut acrofs the fciatic nerve of a living frog, I 



* could not perceive that limb fmaller than the other ; yet it conti- 

 ' nued to be infenfible and motionlefs. Nay, when I had broken 



* the bones of the infenfible limb, or wounded the fkin and flefli, 1 

 ' found that the callus formed, and the wounds healed, as readily as 

 'if the nerve had been entire. The event was the fame after di- 

 ' viding, tranfverfely, the lower or pofterior end of the fpinal mar- 

 ' row of the frog. 



* ' It is well known,' concludes our author, * that, if powder 



* of madder root is mixed with the food of a young animal, the 

 ' bones become red ; or, if a bone has been broken, that the callus 

 'joining its parts will be red. The ferum of the blood, in the firft 



* place, is deeply tinged ; but the red colour of the bones is not fole- 

 ' ]y, nor even chiefly, owing to the coloured ferum or blood circu- 



* lating; for I have found, that, after injeding water into the veflels 

 ' till thefe were emptied of the blood, and that the water came out 

 ' colourlefs, the tinge in the bones appeared equally deep, and was, 

 ' therefore, plainly owing to a great quantity of the red earth added 

 ' to the bones in the time of their growth. But this earth was not 



* tranfmitted by the nerves ; for the colour of thefe, as I found, re- 



* mained unchanged.' 



That the nutritious particles of food are conveyed by the arteries, 

 and applied by their extremities to the various parts of animal bo- 

 dies which require to be repaired or expanded, is an opinion not 

 only bed fupported by fads, but adopted by all the more rational 

 phyfiologifts. The principal fads and arguments in fupport of this 

 theory fhall now be mentioned. 



D d 4 The 



