ABSOHrTIOX OF EOXE. 105 



silver or platinum put round the wing bone of a growing- pigeon, 

 becomes covered with new bone from without, and the original bone 

 included within it gets thinner, or, according to Duhamel, who first 

 made the experiment, is entirely removed, so that the ring comes to lie 

 within the enlarged medullary canal. 



Madder given to an animal along- with its food tinges those parts in which 

 deposition of new bone is taking place. The earth of Ijone apjaears to act as a 

 sort of mordant, uniting with and fixing the colouring matter : and. as in this 

 way the new osseous gro^i;h can be readily- distinguished from the old. advantage 

 was taken of the fact by Duhamel. and afterwards by Hunter, in their inquiries 

 as to the manner in which bones increase in size. By their experiments it was 

 showTi that when madder is given to a young pig for some weeks, the external 

 13art of its bones is deeply reddened, jiroving that the new osseous matter is 

 laid on at the surface of that previously formed. Again, it was found that, 

 when the madder was discontinued for some time before the animal was 

 killed, an exterior white stratum (the last fonned) appeared above the red one, 

 whUst the internal white part, which was situated within the red. and had 

 been fonned before any madder was given, had become much thinner ; showing 

 that absoqition takes place from within. In this last modification of the experi- 

 ment also, as noted by Hunter, a transverse red mark is obseiwed near the ends 

 of the bona, beyond which they are white ; the red part indicating the growth 

 in length dimng the use of the madder, and the white beyond, that which has 

 taken place subsequently, — thus showing that the increase in length is caused 

 by the addition of new matter to the extremities. But other changes take 

 place in the bone. The spaces in the cancellated structui-e, as well as the 

 medullaiy canal, become enlarged by absori^tion ; whilst in other parts the tissue be- 

 comes more compact by farther deposit on the inner surface of the vascular cavities. 

 Tlie sides of the shaft in particular acqiiire greater solidity by the narrowing of 

 the Haversian canals, within which the osteoblasts continue to deposit fresh 

 laj-crs of bone ; and madder administered while this process is going on. colours 

 tlie interior and recently-formed laminae, so that in a cross section the Haver- 

 sian apertures appear surrounded with a red ring. 



Flourens,* and more recently. KoUiker, have repeated and varied these experi- 

 ments, and have represented the results in l^eautiful delineations. KoUiker has, 

 in addition, carefully investigated the microscopic appearances observed in the 

 process of absorption of bone. From the results of his researches (which were in 

 part anticipated by those of Loven) .f it would seem that tlie process is essentially 

 dependent on the presence of large multi-nucleated cells, by him tenned " osto- 

 clasts" (the myeloplaques of Robin), which excavate, in the part which is 

 undergoing absorption, small shallow pits (fovcolcz) in which also they lie. 

 Tliese pits were first noticed by Howship : they seem to occui" wherever 

 absolution is proceeding, and it is to them that the festooned appearance of 

 the Haversian spaces is due. The ostoclasts (fig. 63) vary in size, but are alwaj-s 

 many times larger than a blood-coi-puscle : in shape they are almost always flat- 

 tened, with either an even or an irregular outline. Their substance is granular, 

 and they each contain from two to ten clear round nuclei, but this number 

 may be considerably exceeded. The ostoclasts frequently present on the side 

 hy which they are in contact with the bone a thickened striated border 

 (fig. G3, a), somewhat similar to the well-known thickened base of the columnar 

 epithelium cells of the intestine. "With respect to the origin and destiny of the 

 ostoclasts, they are regarded by KoUiker both as in the first instance derived 

 from and as eventually breaking tfp into osteoblasts. ■\Vegner.+ on the other hand, 



observed that the addition of new bone was much greater at the upper end. Humphiy 

 has foxmd that in the femur the elongation is gi-eater at the lowei; and in the humerus 

 at the iq:)pcr end of the shaft (^led. Chir. Trans., vol. xliv.). 



* Recherches sur le Developpement des Os et des Dents. Paris, IS 42. 



+ Loc. cit., I860. 



1 Virch. Archiv. Ivi. 1873. 



