VITAL GROWTH AND CRYSTALLIZATION 29 



obstruction in the gelatin which prevents the crystal from 

 growing freely? 



Yes indeed! The gelatin forms a network resembling a 

 honey comb which holds the crystals in its meshes. This 

 net can be seen under a powerful microscope, magnifying 

 more than 2,000 times, when a gelatin solution is spread out 

 in a thin layer upon a glass plate and allowed to dry (Fig. 

 13). It is not surprising that a crystal growing in such a 

 net is broken into small units which are attached one to the 

 other as the growing crystal works its way through the net. 



Fig. 13. Honey-comb Structure as Appearing en Many 

 Gummy Solutions 



Structures similar to the one here appear in solutions of gelatins, starch, 

 or gums, if spread out in thin layers on a slide and viewed under high 

 magnification. This one has been magnified 1,380 times. 



[Figs. 13, 14, 16, 17, 18 and 19a are microphotographs from O. Bi'itschli's 

 Atlas zu den Untersuchungen tiber Strukturen, Leipzig, 1898.] 



Such a network is formed not only in gelatin, but also in 

 any other slimy material, such as egg white or various lac- 

 quers like shellac. Moreover, the gelatin or other organic 

 material attaches itself to the surface of the growing crystal, 

 and in this way blocks the growth and development of salt 

 crystals. This interference with crystallization through 

 blocking of the surface of the crystals plays an important 

 role in Pfeiffer's "sensitive crystallization." 



The network of the gelatin is by no means invariably of 

 a simple uniform pattern. It may be modified under the 



