352 



TECHNOLOGY OF DIATOMS. 



or withdrawing both together, the desired part of each can be 

 brought under the objective. 



This mode of operation suffices 

 when you are making preparations 

 of isolated specimens, but when you 

 are making systematic preparations, 

 that is to say, when groups of a 

 number 



classed 



certam number ot species, 

 in a certain order, are to be made, 

 the use of a movable stage is abso- 

 lutely necessary. 



I give a sketch of a stage of this 

 kind which I have constructed, and 

 which has done me good service. 

 In this stage, the height of the box 

 carrying the hollowed rings for hold- 

 ing the prepared cover-glasses is so 

 arranged that the surface of these is 

 on the same level with that on which 

 the Diatoms are spread, and this 

 prevents any change of position, 

 however long the work may have 

 to be continued. 



Cements used for fixing the 

 Diatoms on the Cover-glasses. 



The liquids or cements used for 

 fixing the Diatoms are of various 

 kinds. Some of them change as 

 they grow older, and lose, if not 

 totally, at least a part of their adhe- 

 siveness. Gum-lac is of this class. 

 In general, the cements present a 

 dry surface, from which it is possible 

 to remove dust that may have acci- 

 dentally fallen on it — such are cer- 

 tainly preferable to all others. 



