TISSUES OF THE BODY. 



173 



(fig. 161), arid whose partial origin in the manner just mentioned is at 

 least very probable. 



In many cartilages besides, which are on their way to dissolution, 

 and where a lively change of tissue is commencing again, there often 

 occurs a very extensive segmentation of cells. This is especially the 

 case where in the foetus the production of bone begins at the expense 

 of, and together with, softening of the cartilages. It was formerly sup- 

 posed that other tissue elements (medullary cartilage cells), allied to lym- 

 phoid corpuscles, could spring from the daughter-cells. These were then 

 believed to take part in the formation of other tissues, such as the bony, 

 fatty, and connective. We shall refer again to this in dealing with osteo- 

 genesis. 



106. 



The nature of cartilage, as that of a very early formed and rapidly 

 senescent tissue, explains the fact that, in examining, not alone the 

 mature or aged body, but also the foetal in part, we encounter a series of 

 changes in the tissue in question, which, occurring more rarely in other, 

 parts, are usually looked upon there as pathological occurrences, but which 

 may here be set down for the greater part as normal processes, and must, 

 therefore, be discussed here. 



The transformations which may affect the cell and ground-substance in 

 various ways are more especially three -fatty infiltration, calcification, 

 and softening. They occur principally, but not exclusively, in hyaline 

 cartilage. 



Fatty deposit may commence, as, for instance, in the human costal cartil- 

 ages, even in infancy (fig. 164 a, b). We first remark very small isolated 

 globules of oil, which either lie separately in the body of the cell or 

 grouped around the nucleus. On their becoming more numerous, they 

 coalesce, forming drops of 

 greater magnitude, which 

 either lie in the cavity of 

 the cell, without order, or, 

 more frequently still, they 

 so envelope the nucleus that 

 it cannot be recognised with- 

 out the aid of reagents. Thus 

 it was that that view, held by 

 earlier authors, originated, 

 namely, that the nucleus 

 could itself be transformed 

 into an oil-globule. Should 

 the process advance very far, 

 almost the whole cavity of 

 the cell may eventually be 

 occupied by one large drop 

 of oil, or a swarm of globules. 

 Calcification of cartilagi- 

 nous tissue is essentially 

 different from true ossifica- 

 tion, that is, from the for- 

 mation of genuine bony sub- 

 stance containing peculiar cells, although both processes were formeily 

 confounded with one another. 



Fig. 164. Costal cartilage of an infant, transversely cut. 

 a, a portion from the circumference ; b, from the interior. 



