ON THE BONES OF ANIMALS. 407 



it enlirely difappeared. According to the experiments of ihefe 

 gentlemen, other vegetable dyes, fuch as logwood, turmeric 

 and alkanet root, did not communicate their refpedive tints 

 to the bones.* 



This effeO. of madder upon the bones, was foon afterwards Du Hamel ufed 

 made ufe of by Du Hamel, in his attempt to prove the man- 5hew^Jhr'rowth 

 ner in which the bones of animals are encreafed in thicknefs. of bones. 

 Obferving in the vegetable kingdom, that the bark, by a fort 

 of fecretion, formed the ligneous part of a tree, in fucceffive 

 layers ; fohe conceived that the periofteum, or membrane fur- 

 rounding bones, being converted into offeous matter, en- 

 creafed their diameter by adding to them concentric lamina: 

 in fucceffion. In order to prove the jufinefs of his opinion, he 

 mixed the food of a cock with madder root for a month, with- 

 held it for a month, and then gave it again. He afterwards 

 killed the animal, and upon infpe£lion thought he obferved the 

 Appearance which he expefied ; viz. two layers of red bone 

 inclofing one of white, correfponding to the periods of the 

 madder's being given or withheld. 



This experiment, and fome others related by Du Hamel, It is very doubt- 

 appear to be conclufive in favour of the theory, which |ie ^"' whether that 



growth could be 

 wifhed to eftabliOi; and as they were conduced by a phylio- fo indicated. 



logifi: of high character, the accuracy of the obfervations could 

 not have been doubled, had thefe experiments ftood alone. 

 But when they are compared with fome of his own previous 

 experiments, and thole of other authors, it is difficult to re- 

 concile them. In fome of Du Hamel's experiments, for in- 

 ftance, the bones of a cock were tinged of a rofe-colour 

 through their whole fubftance in fifteen days, and thofe of 

 young pigeons of a deep fcarlet in three days. In feveral ex- 



• From fome experiments I made on young pigeons, I found 

 that a confiderable quantity of logwood, in the form of extract, 

 communicated an evidently purple tint to the bones. With regard 

 to turmeric, it appears to be altered in its colour by palling through 

 the digeftive organs^ for the fceces of the animals, who took it in 

 confiderable quantity, were conrtantly green : whilft either log- 

 wood or madder root exhibited their refpeilive hues after paiTing 

 through the inteftlnes. Saffron exhibits properties different from 

 any of thefe fubftances ; iv though a pigeon took it in confider- 

 able quantity, and thereby had its foeces ringed, yet no perceptible 

 alteration of colour was produced in its bones. 



F f 2 perimenls 



