b THE PREPARATION OF MICROSCOPICAL OBJECTS. 



8. When examining an object, keej) one hand on the fine 

 adjnstment, and keep screwing it up and down shghtly the whole 

 time: in this way 2^'^^ts of the object at different depths are 

 brought into focus successively, and a clearer idea of the object 

 is obtained. 



9. If the object appears dim or dirty, find out where the 

 fault lies in this way : — 



While looking down the microscope, turn round the eyepiece 

 with your right hand : If the dirt turns round too, remove and 

 clean the eyepiece. If the fault is not in the eyepiece, move 

 the slide about gently; if the dirt moves with the slide, remove 

 the slide and clean it. If the dirt does not move with either 

 the eyepiece or the slide the fault is almost certainly in the 

 objective, which should be removed and examined; if dirty, it 

 must be cleaned very carefully with a j)iece of silk or chamois 

 leather. 



VI.-THE PREPARATION OF MICROSCOPICAL OBJECTS. 



In mounting microscopical objects be careful that your slides 

 and coverslips are thoroughly clean. Slides should be labelled 

 as soon as they are prepared, and should be kept in a box or 

 cabinet in w^hich they lie flat. 



A. Methods of Mounting. 



There are various media in which objects may be mounted. 

 The method of procedure is much the same with all. Put a, 

 small drop of the fluid in the middle of the slide, place the 

 object in the middle of the drojD, and arrange it with needles in 

 the position desired. Then place the cover glass carefully on 

 the top, letting it rest by one edge on the slide and supporting 

 the opposite edge by a needle : withdraw the needle gradually 

 so as to let the cover-glass down slowly, and drive out any air- 

 bubbles there may be in the fluid. If any air-bubbles still 

 remain, leave them alone, as they will jjrobably work out by 

 themselves. Be careful not to use too large a drop of your- 

 mounting medium, and above all things be careful not to let 

 any of it get on the top of the cover-glass ; should this happen,, 

 the cover-glass must be removed at once and the specimen 

 mounted afresh with a clean one. 



The most important mounting media are the following. 



