32 - LECTURE II. 



periosteum is that membrane in wliicli the vascular system of a bone 

 undergoes the amount of subdivision which reduces its capillaries to 

 the dimensions suited for penetrating the pores leading to the vascular 

 and Haversian canals. 



These preparations of the bones of young pigs fed with madder 

 (Nos. 190 — 201. Phys. Series), and those of young birds, showing 

 artificial perforations (Nos. 188^ 189.), illustrate some experiments 

 by Hunter on the growth of bone. 



The strong affinity of phosphate of lime for the colouring matter 

 of the Rubia tinctorum, which, when taken as food, passes into the 

 plasma of the circulating fluids and combines with the phosphates of 

 lime with which that fluid comes in contact, has been supposed to 

 throw some clear light upon the growth of bone. All the phosphate 

 of lime which is deposited in tooth or bone, whilst the madder is in 

 the system, is deeply tinged by it, and Hunter found that the exterior 

 layers of the growing bone of a young pig which had been fed a 

 fortnight on madder were most strongly coloured. But he observed 

 also in another young pig similarly fed, but killed a fortnight after 

 the madder had been omitted from its food, that " the exterior of the 

 bones was of the natural colour, but the interior red." (xi. p. 75.) 

 The inference deduced was, that a new layer of bone, during the 

 absence of madder from the circulating system, had been formed, 

 uncoloured, on the exterior surface. 



Mr. Gibson endeavoured to invalidate the conclusion, by hinting 

 that the colouring matter might have been removed from the pre- 

 viously stained bone by the serum of the blood, which fluid he be- 

 lieved to have a greater affinity for the dye than phosphate of lime 

 had; but Mr. Paget has proved by experiment that the phos- 

 phates have actually the stronger affinity for the dye. 



The well-known fact that the phosphates on every internal or 

 external surface of the bone, which is exposed to the current of the 

 dye-charged plasma, attract the dye, by no means invalidates the con- 

 clusions from the ingenious experiments of Hunter ; for the quantity 

 of colour so imbibed by the previously and completely formed bone 

 is always much less than that which the growing bone receives from 

 the phosphates deposited during the presence of madder in the cir- 

 culating system. 



Hunter's experiments, therefore, coincide with those of Du Hamel, 

 made by encompassing shafts of growing bones with rings of wire, 

 in proving that the increase in circumference is due to growth at the 

 periphery beneath the periosteum, such i-ings having been found, 

 after a certain period of growth, in the cavity of the enlarged bone. 

 The growth in length is, however, much more active ; and this, in 



