6 



Making Wholemounts 



The last few chapters have surveyed a few of the reagents and processes 

 used in the preparation of microscope sHdes. It is now time to turn to the 

 preparation of the slides themselves. Those described in this book are prepared 

 in any one of three ways. First there are "wholemounts" which, as the name 

 indicates, are mounts either of whole organisms or of parts of organisms 

 which are sufficiently small or transparent to be studied without specialized 

 treatment. Slides of the second type, described in the next chapter, are "smears" 

 in which a thin layer of some fluid intended for study is spread upon a slide 

 and there stained and mounted. Preparations of the third type are "sections" 

 which are thin slices cut from an object either too thick or too complex to be 

 studied as a wholemount; the preparation of sections is described in Chapter 8. 

 Wholemounts are the easiest of all slides to prepare and should be the first 

 to be made by the beginner. 



Temporary Wholemounts. Temporary wholemounts are prepared by every 

 student for the purpose of examining material under a microscope. No object 

 should ever be examined on a slide until the coverslip has been placed over 

 it. The purpose of the coverslip is not only to prevent water from condensing on 

 the lenses but also to provide a flat surface for observation. Temporary whole- 

 mounts are usually prepared in water by the simple process of taking a drop 

 of the fluid containing the material to be examined, such as living Paramecium, 

 and lowering the coverslip on the surface. This is perfectly satisfactory, pro- 

 viding it is not necessary to observe the objects for long periods. After a time, 

 however, the water evaporates from the edges of the coverslip, which crushes 

 the material. This may be avoided readily by slowing the evaporation with 

 petroleum jelly, a little ring or square of which is built up in the center of the 

 slide before the drop is placed in position. The coverslip is pressed down very 

 gently, until it is seen to be sticking to the petroleum jelly. 



There are many tricks which may be used to examine animals that move 

 too rapidly for study. One of the simplest of these is to place a piece of lens 

 paper on the slide and then to place a drop of the culture under examination 

 on this. The addition of a coverslip causes the fibers of the lens paper to 

 make, as it were, a series of little compartments in which the animals become 

 trapped. Another useful device is to mix thoroughly a culture of the animal 

 in question with an equal volume of 0.5 per cent agar. This thickens the 

 liquid sufficiently to slow down most forms. 



The term wholemount, however, usually means a permanent preparation 



39 



