TISSUES OF THE BODY. 205 



are often enveloped in and traversed by tracts of fatty tissue. We 

 have already alluded to the same kind of transformation between the 

 elements of muscle (fig. 194). Here (fig. 198) may be seen all the 

 transitions from connective-tissue corpuscles to fat-cells in the loose 

 connective- tissue situated in fleshy substance. We see the first of 

 these (a) becoming gradually filled with small and large globules (I). 

 which commence to fuse with one another. Owing to this, cells origi- 

 nally fusiform become expanded gradually (c) into the spherical form 

 of the fat-cell. Here, then, we have fat-cells springing from connective- 

 tissue corpuscles, an occurrence which has also been observed by Furster 

 in the formation of lipomas. 



The question also as to whether fat-cells may again undergo retrograde 

 development into ordinary fusiform and stellate connective-tissue cells, 

 may be answered in the affirmative. Thus Kolliker observed, after 

 disappearance of the fatty matter of the subcutaneous cellular tissue, 

 the so-called serous fat-cells ( 121) become transformed into such con- 

 nective-tissue corpuscles. The same may be seen under similar circum- 

 stances around the hilus of the kidney and under the pericardium, where 

 the fatty tissue is transformed into a regular mucoid tissue (VircJiow). 



9. Connective-Tissue. 

 125. 



Under the name of connective-tissue is understood a substance widely 

 distributed throughout the body, consisting, like those structures already 

 considered, of cells or their rudiments and intercellular matter. The 

 latter, however, is here glutin-yielding, and indeed affords almost always 

 collagen, except in rare and exceptional cases, such as the cornea, where 

 chondrin is obtained from it. It is likewise characterised by its ten- 

 dency to break up into fibres, which latter process has already taken 

 place, more or less, in every well-developed connective-tissue, giving rise to 

 connective-tissue fibrillas and fasciculi in a structureless substance. Again, 

 there appear in this tissue elastic elements besides, which have originated 

 in the metamorphosis of the intercellular matter. They enter into the 

 formation of fibres, networks of the latter, fenestrated membranes, ter- 

 minal layers around fasciculi of connective-tissue and interspaces, which 

 may harbour cells. 



Now, although it is thus possible to characterise in a few words the 

 peculiarities of most parts of the body consisting of connective-tissue, 

 and though, from this point of view, the latter may be looked upon, in 

 many cases, as only a higher stage of development of that substance, 

 described in a previous section as gelatinous tissue, still we must remember 

 that many parts formed of this tissue differ more or less from this plan 

 which we have just given, and may deviate even so far as to be beyond 

 being recognised as belonging to it. Connective-tissue appears indeed 

 in such a variety of forms that its limits arc rather difficult to define, and 

 every histologist of the present day gives the name connective-tissue to 

 tilings which are frequently very remote from what was considered such 

 at an earlier microscopic epoch. 



If we now inquire, in order to obtain a clue through the difficulties of 

 the coming description, what these modifications are, the following points 

 may be noticed. 



