Making Wholemounts 109 



There are many tricks that 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. For 

 the same purpose, 0.1 per cent carboxymethyl cellulose may be used. 



The term wholemount, however, usually means a permanent prepara- 

 tion made in a medium that will both preserve the object and hold the 

 coverslip in place. These mounting media are either water-miscible, in 

 which case most objects can be placed in them directly, or resinous, re- 

 quiring extensive preparation of the object. Each type will be described 

 in its turn. 



MOUNTING IN GUM MEDIA 



The simplest preparations are those made in water-miscible mountants, 

 which are of far wider utility than is usually realized because of a com- 

 plete mental block on the part of most microscopists when faced with any 

 mounting medium that is not a solution of a resin in a hydrocarbon. As a 

 matter of fact, most simple objects, such as the scales of fish and animal 

 hairs, may be mounted more readily in aqueous than in resinous media. 

 This process of mounting is so simple that it is regarded with distrust by 

 those who have come to believe that only through complexity can good 

 results be produced. With aqueous media the object to be mounted is 

 merely placed in a drop of mountant on the slide, and a coverslip is 

 pressed on top. This process, moreover, is not confined to relatively hard 

 objects but may be applied to many protozoa and other small inverte- 

 brates. Small invertebrates do not always make satisfactory permanent 

 mounts by this method, for they ultimately reach a refractive index identi- 

 cal with that of the mountants and thus vanish. A temporary mount of a 

 Paramecium in one of these media, however, will show the internal struc- 

 ture better than will the average stained mount, while it will also give a 

 clearer indication of what the living object looked like. The most com- 

 mon objects to be mounted by this method are small arthropods; a de- 

 scription of the preparation of a mite in one of these media is given in 

 Part Three. 



Finishing Slides in Gum Media. Slides may be left exactly as they are 

 prepared, but this will give a rather clumsy appearance, since some of the 

 mountant will exude from under the coverslip. This exudate may be re- 

 moved by washing with warm water, but it will be some time after this 

 before the gum at the edges of the coverslip is dried. Moreover, no mount- 



