MICROSCOPIC OBJECTS. 125 



a common or native oyster, or a muscle, just opened, and 

 cut off a smaU portion of that part commonly called the 

 beard ; a piece about a quarter of an inch over is amply 

 sufncient. Place this in an aquatic live-box with a little 

 of the hquor of the oyster or salt and water, taking care 

 to have only one lamina, and spreading it out flat ; then 

 put the cover on. Now place it under the microscope, 

 adjust to focus, and let the edge of the beard pass across 

 the middle of the field of view, when the currents will be 

 distinctly observed.. A little indigo mixed in the water 

 enables the currents to be better observed, but they will 

 not continue so long as without that coloured material. 

 The motion will often continue for more than an hour 

 after the specimen has been separated from the animal. 

 The vision is much improved by the judicious introduction 

 of stops or diaphragms under the object and stage. On 

 the subject of viewing the currents in Fluids during their 

 evaporation, see 'Microscopic Illustrations,' page 143. 



