258 COLLOIDS IN BIOLOGY AND MEDICINE 



are more beautiful and possibly more natural. In two weeks the 

 structures attain a height of from 5 to 10 cm. 



The growths described above offer analogies to organisms which 

 are completely surrounded by water only, yet there are those which 

 offer a resemblance to the growth of terrestrial plants. We might 

 mention the " blossoms" of many crystalloid substances, especially 

 the ammonia salts. H. WiSLicENUS* 1 has thoroughly studied the 

 growth and structure of fibrous alumina. If granules of aluminium 

 which have been activated by contact with traces of mercury subli- 

 mate, for example, are permitted to lie in a moist place, very soon 



FIG. 44. Fibers of fibrous alumina, magnified X 40. (From H. Wislicenus.) 



fibrous structures grow from the metal, which in a few hours may 

 reach more than 1 cm. in length. Under the influence of the mercury 

 as a catalyzer, aluminium oxid is formed from the aluminium accord- 

 ing to the formula: 



Al + 3 H 2 = Al (OH) 8 + 3 H. 



In this instance it is not the osmotic pressure of entering water 

 which bursts the films, thus bringing a fresh metal surface to the 

 reaction, but the pressure of the hydrogen gas. 



Though in this case, as well, there are many gaps in the resemblance 

 to natural organisms, nevertheless the fibers formed show certain 

 resemblances to real fibers (see Figs. 44, 45). 



