GROWTH AND ABSORPTION OF BONE. 



281 



become much thinner ; showing that absorption takes place from within. In this 

 last modification of the experiment also, as noted by Hunter, a transverse red mark 

 is observed near the ends of the bone, beyond which they are white ; the red part 

 indicating the growth in length during 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. Madder administered 

 while the process of formation of the concentric lamellae of the Haversian systems 

 is going on, colours the interior and recently-formed laminae, so that in a cross 

 section the Haversian apertures appear surrounded with a red ring. 



Flourens, and more recently, Kolliker, have repeated and varied these experi- 

 ments, and have represented the results in beautiful delineations. Kolliker 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), it would seem that the process is essentially 

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

 clasts," identical with the " myeloplaxes " of .Robin (see p. 267), which excavate, in 



Fig. 320. THREE OSTOOLASTS FROM ABSORPTION SURFACES OF GROWING BONE. 400 DIAMETERS 



(Kolliker). 

 a, with thickened striated border. 



Fig. 321. BONY TRABECUTLA FROM THE LOWER JAW OF A CALF EMBRYO WITH HOWSHIP'S FOVEOL.E AND 



GIANT-CELLS AT THE ENDS WHERE ABSORPTION IS PROCEEDING AND OSTEOBLASTS COVERING THE 

 SIDES WHERE BONK IS BEING DEPOSITED (Kolliker). 



the part which is undergoing absorption, small shallow pits (foveolce) in which also 

 they lie. These pits were first noticed by Howship : they seem to occur wherever 

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

 Haversian spaces (p. 2G4) is due. The ostoclasts (figs. 320, 321) vary in size, but are 

 always many times larger than a blood-corpuscle : in shape they are spheroidal or 

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

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

 number may be considerably exceeded, whilst on the other hand, there may be but 

 one large nucleus provided with a number of bud-like projections. The ostoclasts 

 have frequently on the side by which they are in contact with the bone a thickened 

 striated border (fig. 320, 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 Kolliker both as in the first instance 

 derived from and as eventually breaking up into osteoblasts. Ostoclasts are found 

 in connection with the roots of the milk teeth where these are undergoing absorp- 

 tion to make way for the permanent set. They were also noticed by Billroth to 

 produce absorption of ivory pegs which had been driven into bone. Precisely 



