OF NATURAL HISTORY. 217 



« Iv, the lower or pofterior end of the fpinal marrow of the 



* frog. 



< It is well known/ concludes our anther, ^ that, if pow- 



< der of madder root is mixed with the food of a young ani- 



< mal, the bones become red ; or, if a bone has been brok- 

 « en, that the callus joining its parts will be red. The ferum 



< of the blood, in the firfc place,, is deeply tinged j but the 



* red colour of the bones is not folely, nor even chiefly, owln^. 



< to the coloured ferum or blood circulating ; for I have 

 « found, that, after injecting water into the vciTels till thefo 

 ' 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 eartli was not tranfmitted by the nerves ; for the 

 ' colour of thefe, as I found, remained unchanged.' , ,- 



That the nutritious particles of food are conveyed by the 

 arteries, and applied by their extremities to the various parts 

 of animal bodies which require to be repaired or expanded, 

 is an opinion not only befi: fupported by facls, but. adopted 

 by all the more rational phyfiologiflis. The principal fa(^g 

 and arguments in fupport of this theory fliall nov/ be m,en- 

 tioned. 



The chyle, as form^erly remarked, is converted into blood » 

 The glutinous part of the blood, known by.the nameof 

 cGagulablc lynph^ refembles the white of an ^"^g. That the 

 white of an egg is the fole nouriihment of the chick before 

 its exclulion, is an eftablifiied facl ; and the conclufion, from 

 analogy, that the lymph of blood is deftlned for the growth 

 and reparation of animal bodies, is by no means unnatural. 

 « Without repeating,' fays Dr. Monro, < our extreme uncer- 

 « tainty as to the tubular nature of the nerves, and the im- 

 ^ probability that canals {o exceedingly minute as thofe with- 



* in the nerves muft be, and of fuch length, are deiiined iox 



