154 METHODS OP MICEOSCOPICAL RESEARCH. 



stage, and K is a piece of glass (its termination 

 being represented by a dotted line) which slides 

 into grooves in the sides, J J, and which is intended 

 to secure, and practically does secure, absolute 

 cleanliness to the slide during its preparation. 



Now, the stage being fixed in its place by its two 

 screws, an ordinary glass slip (3 in. by 1 in.) is taken, 

 and by means of a turn-table a very minute circle 

 is marked, with a writing diamond, precisely in its 

 centre, upon this circle is placed the smallest 

 possible drop of distilled water, and upon this drop 

 of water the cover, on which the diatoms are to be 

 mounted, is placed, and of course firmly held in 

 its position by capillary attraction ; care must be 

 taken that the circle on the slip shall exactly coin- 

 cide with the centre of the cover. The slip is then 

 to be placed under the springs E E, and the stage 

 must be so fitted to the microscope that when the 

 rim F of the sliding portion of the stage is drawn 

 down by the handle Gr it is stopped by a pin L 

 when the small circle under the cover on the slip 

 is precisely in the centre of the field of the micro- 

 scope. The slip being firmly held in its position 

 by the springs E E the absolute centrality of the 

 "mount" is ensured, if care be taken that the 

 cover is not moved. Now, having spread and 

 dried some diatoms upon another slip, place the 

 slip upon the lower portion of the frame C C. This 

 slip can be freely moved, and if the screw I is 

 screwed out to its extreme length it is obvious that 

 if the frame C C is raised to the lower end of the 

 screw the lower edge of the movable slip can be 

 passed across the field of the microscope and any 

 desired diatoms selected from it. After removing 



