s> 



TISSUES, ORGANS, AND systems. 61 



diameter from immeasurable fineness up to Fj 22 



a thickness of 0-003'", and even 0005'" (in .. , i i ; 

 animals even to as much as 0-008'"), and \. I Jv* 



when they are present in quantity, exhibit a \ \( \ 

 yellowish colour. These so-called elastic i\ 



fibres are, when perfectly formed, quite 

 solid, but may subsequently acquire little /' j'v 

 cavities in particular spots; and these, in /' /, ~ ; ;o.w v y\ 

 one animal, the Giraffe (Quekett, ' Histo- , J-\ 

 logical Catalogue/ i), are so regular, that the j ^\i \] 



fibres present a pretty transversely striated 

 appearance. The margins of the elastic fibres are in general 

 quite rectilinear, but in some rare cases appear to be notched 

 and even, asYirchow saw them, in newly-developed tissues, beset 

 with a great number of shorter and longer pointed processes. 

 Hitherto the elastic fibres have been separated from the nucleus 

 fibres : since, however, the latter are distinguished from the 

 former in nothing but their diameter; furthermore, as all elastic 

 fibres are originally as fine as nucleus-fibres ; and since, finally, 

 the latter are not formed of nuclei alone, it will be better 

 wholly to suppress the name of nucleus-fibres, and to divide the 

 elastic fibres simply into finer and coarser. The elastic fibres 

 are found either isolated as longer or shorter fibres, which may 

 be straight or wind spirally round other parts (bundles of con- 

 nective tissue, nerves), and in this case they are commonly of the 

 finer kind j or by the anastomosis of fibres of different sizes, a 

 so-called fibrous elastic netivork is formed, which is sometimes 

 expanded in a membranous form, and sometimes penetrates other 

 tissues to various depths. A modification of this fibrous elastic 

 network is formed by the elastic membranes, in which the 

 fibres are so closely interwoven, that a connected membrane 

 arises, which in the most extreme cases no longer exhibits any 

 indication of its previous nature, and appears as a perfectly 

 homogeneous membrane with smaller gaps (the fenestrated 

 membrane of Henle). 



Chemically, elastic tissue presents very decided reactions, 

 but the composition of its substance is not yet exactly known. 

 In cold concentrated acetic acid, the elastic fibres, except that 



Fig. 22. Elastic network from the tunica media of the pulmonary artery of a horse, 

 with lacunae in the fihre, x 330. 



