VARIETIES OF CONNECTIVE TISSUE. 63 



present * Von Wittich-f- has described the effects of electrical 

 excitation of the pigment cells of Hyla arborea, which appear 

 to be most sensitive to it. 



In adult specimens of Rana esculenta and temporaria, and 

 also in Tritons, notwithstanding repeated trials, I was unable to 

 perceive that any influence was exerted on the pigment cells 

 by the action of induction shocks of electricity. R. Wagner 

 has observed the presence of stellate pigment cells possessing 

 extraordinary motility in Cephalopods. 



THE VARIETIES OF CONNECTIVE TISSUE. In its first forma- 

 tion, and during the earliest stages of its development, connec- 

 tive tissue consists of cells which, for the most part, lie closely 

 compressed together ; it then presents a parenchymatous appear- 

 ance, similar to that observed in the embryonic tissue of certain 

 neoplastic formations, as the small-celled sarcoma of Virchow.J 

 Apart from this form of connective tissue, to which we shall 

 again refer in the history of its development, that of the adult 

 organism can be arranged under two heads ; one of which in- 

 cludes those varieties of networks and trabeculse that are deve- 

 loped from cells, whilst the other includes the fibrillar connective 

 tissue, characterised by the presence of peculiar invariably un- 

 branched fibres (connective tissue fibrils) composed of a gelatine- 

 yielding substance. 



Connective-tissue Plexuses and Trdbeculce. These forms 

 do not yield gelatine on boiling. They either occur in large 

 independent masses, or they contain other tissues, to which 

 they give support and covering, in the lacunse of their meshes, 

 which are sometimes more delicate and sometimes coarser. 



a. In the former case the connective tissue is usually cha- 

 racterised by its succulency and its ready compressibility. The 

 larger masses are transparent, or at least very translucent, and 

 on section, in consequence of the escape of fluid, easily collapse 

 (gelatinous tissue of Virchow). On the addition of acetic acid, 

 a flocculent and threadlike precipitate of Mucin can frequently 

 be obtained in considerable quantity from the escaped fluid 



* Briicke, loc. cit. 



t Von Wittich, Muller's Archiv, 1854, p. 41. 



| Die Krankhaften geschiciilste, Bd. ii., p. 224, fig. 140. 



