FIBRES OF ELASTIC TISSUE. 133 



cell-tubules of connective tissue usually are, and the 

 transformation of these latter into the former can gradu- 

 ally be traced with such distinctness, that there remains 

 no doubt, that even the coarser elastic fibres directly 

 result from a chemical change and condensation of the 

 walls of the cells themselves. Where originally there 

 lay a cell, provided with a delicate membrane and 

 elongated processes, there we see the membrane gradu- 

 ally increasing in thickness and refracting the light more 

 strongly, whilst the proper cell-contents continually 

 decrease and finally disappear. The whole structure 

 becomes in this way more homogeneous, and to a certain 

 extent sclerotic, and acquires an incredible power of 

 resisting the influence of reagents, so that it is only 

 after long-continued action that even the strongest 

 caustic substances are able to destroy it, whilst it com- 

 pletely resists the caustic alkalies and acids in the 

 degree of concentration usually employed in microscopi- 

 cal investigations. The farther this change advances, 

 the more does the elasticity of the parts increase, and in 

 sections we usually find these fibres not straight or 

 elongated, but tortuous, curled up, spirally coiled, or 

 forming little zigzags (Fig. 43, c, e). These are the 

 elements which in virtue of their great elasticity cause 

 retraction in those parts in which they are found in con- 

 siderable quantity, as, for example, in the arteries. 

 The fine elastic fibres, which are those that possess the 

 greatest extensibility, are usually distinguished from the 

 broader ones which certainly do not present themselves 

 in tortuous forms. As far as regards their origin, how- 

 ever, there seems to be no difference between the two 

 kinds ; both are derived from connective-tissue cells, 

 and their subsequent arrangement is only a reproduction 

 of the original plan. In the place of a tissue, consisting 

 of a basis-substance and anastomosing, reticulated cells, 



