STRUCTURES RESEMBLING ORGANIC GROWTHS. 147 



be formed, especially in the case of zinc, as above described; 

 several such structures derived from different filaments may 

 fuse and form a compound vesicular or cellular mass. One of 

 the most interesting modifications is of a kind often shown by 

 surface-filaments of iron or copper ferricyanide, consisting in 

 a series of transverse striations resembling those of a striated 

 muscle fiber. A regular ladder-like structure of this kind may 

 extend for a long distance; it is apparently due to the presence 

 of alternately denser and thinner zones in the precipitation- 

 membrane forming the wall of the tube. This structure is 

 found only in the larger filaments running along the surface of 

 the solution, and indicates that the deposition of precipitate 

 takes place in an intermittent manner under these conditions; 

 the regular rhythmical recurrence of a metastable condition of 

 some kind, such as supersaturat'on as in the phenomenon of 

 the Liesegang rings 1 may determine its production, but the 

 precise conditions require further study. Occasionally the finely 

 divided precipitate inside the tube may aggregate to form rounded 

 masses repeated at regular intervals, in a manner suggestive of 

 a row of spores. 2 Filaments of zinc ferricyanide may at times 

 exhibit a regularly constricted or moniliform appearance, but 

 they never form regular cross-striations like those shown by 

 iron and copper filaments; the coarser texture of the precipitate 

 is probably responsible for this difference. 



Certain other types of precipitation-structure should also be 

 mentioned briefly. 3 Masses of precipitate of a vesicular or 

 chambered rather than filamentous structure are often laid down 

 at the surface of the metal ; this is more frequently the case with 

 zinc than with iron or copper. Apparently in such cases the 

 walls of the first formed vesicles remain intact, and do not rupture 

 to allow the solution of metallic salt to flow out in the continuous 



1 Cf. Liesegang, " Beitrage zu einer Kolloidchemie des Lebens," Dresden, 1909. 

 For a more recent study of this phenomenon cf. Stansfield, American Journal of 

 Science, 1917, Vol. 43, p. i. 



2 The structure of these tubules resembles closely that of the "osmotic stems" 

 described and pictured by Leduc in his "Mechanism of Life," London, 1911, pp. 

 141-2. 



3 In Lehmann's " Molekularphysik" various precipitation-formations are 

 compared with different types of organic structure, and much interesting detail 

 is given. 



