SKELETON OF THE VERTEBRATA. 209 



stances wllh the food of animals the bones will soon become 

 deeply tinged by them. This fact was discovered acciden- 

 tally by Mr. Belchier, who gives the following account of 

 the circumstances that led him to notice it.* Happening 

 to be dining with a calico printer on a leg of fresh pork, he 

 was surprised to observe that the bones, instead of being 

 white as usual, were of a deep red colour; and on inquiring 

 into the circumstances, he learned that the pig had been fed 

 upon the refuse of the dying-vats, which contained a large 

 quantity of the colouring substance of madder. So curious 

 a fact naturally attracted a good deal of attention among 

 physiologists, and many experiments were undertaken to 

 ascertain the time required to produce this change, and to de- 

 termine whether the effect was permanent or only temporary. 

 The red tinge was found to be communicated much more 

 quickly to the bones of growing animals than to those which 

 had already attained their full size. Thus the bones of a 

 young pigeon were tinged of a rose colour in twenty-four 

 hours, and of a deep scarlet in three days; while in the adult 

 bird, fifteen days were required merely to produce the rose 

 colour. The dye was more intense in the solid parts of 

 those bones which were nearest to the centre of circulation, 

 while in bones of equal solidity, but more remote from the 

 heart, the tinge was fainter. The bone was of a deeper dye 

 in proportion to the length of time the animal had been fed 

 upon the madder. When this diet was discontinued, the 

 colour became gradually more faint, till it entirely disap- 

 peared. I shall have occasion in the sequel, to discuss the 

 inferences which have been drawn from these curious facts. 



§4. Skeleton of the Vertchrata. 



The purposes to be answered by the Skeleton, in vertc- 

 brated animals, resolve themselves into the three following; 

 first, the affording mechanical support to the body generally, 

 and also to different portions of the body; secondly, the pro- 



* Philosophical TransucUons for 1736, vol. xxxix. 287 and 289. 



