INTRODUCTION 33 



so useful in the preparation of culture-media for 

 observing the growth of bacteria. The same species, 

 together with another (Gracilaria confervoides, and 

 probably also species of Eucheuma) are used by the 

 Chinese and Japanese for making jellies and sweet- 

 meats, and for stiffening purposes, varnishes, &c. 



The extensive deposits of fossil Diatoms which 

 occur in several quarters of the world furnish in 

 some cases valuable polishing powders, and are used, 

 as in the case of the Hanoverian Kieselguhr deposit, 

 for mixture with nitroglycerine to form dynamite. 



