122 LOCOMOTION. [CHAP.V. 



the increase in their dimensions, occasioning that separation of their 

 nuclei, already described (p. 118, and fig. 30, c). In the long bones 

 this takes place chiefly in the longitudinal direction, which is that in 

 which growth is most active ; and it continues till adult age. This 

 fact has been long ascertained, though its real purpose appears to 

 have been overlooked. Hales and Hunter both inserted metallic sub- 

 stances along the shaft of a growing bone, in a young animal, at a 

 certain distance apart; and found, after an interval of time, that the 

 distance between them remained the same, or nearly so, while the 

 extremities of the bone were much further apart : thus proving that 

 the principal growth had taken place near the extremities. 



Secondly, bones increase in dimension by an accession of new 

 osseous substance on their exterior ; this new substance consisting 

 not merely of new laminae, but of new systems of laminae, and of 

 new involutions of the vascular surface to form new Haversian 

 canals, so that the earlier systems of laminae are covered over by 

 the more recent ones. This has been best proved by the experi- 

 ments with madder. 



It was ascertained accidentally by Belchier that the rubia tinc- 

 torum, or madder, mixed with the food of pigs, imparted its red 

 colour to their bones ; and this circumstance has been ingeniously 

 taken advantage of by several physiologists in the prosecution of 

 researches on the growth of bone.* Duhamel, Hunter, and many 

 others, have performed multiplied experiments of this kind. In the 

 Museum of King's College are some good preparations of bones so 

 acted upon. 



It is found that, in very young animals, a single day sufiices to 

 colour the entire skeleton, apparently in an uniform manner ; in 

 these there is no osseous material far from the vascular surface. 

 But, if we make a transverse section of one of the long bones so 

 treated, we observe the deepest, or even the only colour, to be 

 really on the vascular surface; the Haversian canals are each 



* The colouring of bone by madder results from an affinity of the colouring 

 principle for the phosphate of lime. This opinion was distinctly broached by 

 Haller (El. Phys. t. viii. p. 329), and it was subsequently proved by Rutherford^ 

 who shewed it experimentally. To an infusion of madder in distilled water add 

 muriate of lime : no change takes place. Then add phosphate of soda in solu- 

 tion. By double elective affinity, phosphate of lime and muriate of soda are 

 formed. The phosphate is insoluble, and subsides in union with the coloiu 

 ing matter as a crimson lake. When madder is given as food, its colouring 

 principle is absorbed, and circulates with the blood ; and it colours first that 

 part of the bone which is in course of formation from that fluid, or which has 

 been last formed, i. e. which is nearest the vascular surface. 



