Mounting 



GUM MOUNTS 



43 



ultimate suppression of gum arabic in 

 mounting media. 



Types of Objects Which May Be Mounted 



Simple water-miscible liquid mountants 

 are of far wider utility than is usually 

 realized, for there has been a complete 

 mental block on the part of most micro- 

 scopists when faced with any mounting 

 medium which is not a solution of a resin 

 in a hydrocarbon. As a matter of fact, 

 most simple objects such as the scales of 

 fish, animal hairs, and the like, may be 

 more readily mounted in aqueous media 

 than in resinous ones. The actual 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 these 

 media one merely takes the object which 

 it is desired to mount, places it in the drop 

 of mountant on the shde, and presses a 

 coversUp onto the top. This process is not 

 confined to relatively hard objects of the 

 type described, but may also be apphed 

 to many protozoa and other small inverte- 

 brates. These do not make satisfactory 

 permanent mounts by this method, for 

 they ultimately reach a refractive index 

 identical with that of the mountants and 

 thus vanish; but a temporary mount of 

 Paramecium, in one of these media, will 

 show the internal structure to a class far 



better than will the average stained 

 mount, and will also give a far better 

 reaUzation of what the living object looks 

 hke. Objects most commonly mounted 

 however, are small arthropods of -the 

 degree of transparency that does not re- 

 quire that the skeleton be cleared in the 

 manner described in Chapter 6. 



Gum mountants are not satisfactory in 

 thick layers and the writer has never made 

 a successful mount in a deep cell. There is 

 no point in endeavoring to use shallow 

 cells for these media, for the viscosity of 

 the mountant is sufficiently high to pre- 

 vent the coverslip from crushing small 

 objects. 



Finishing Slides in Gum Media 



Exudate round the edges of the cover 

 may be removed by washing with warm 

 water, but it will be some time before the 

 edges reharden. Moreover, no mounting 

 medium containing glycerol or sorbitol can 

 fail to absorb moisture from the air on 

 humid days, and to lose it on dry days, so 

 that it is usually better to finish the shde 

 by applying a ring of varnish in the man- 

 ner described in previous chapters. It does 

 not matter what cement is employed, the 

 writer's preference being for gold size, 

 probably more from force of habit than 

 from any other reason. 



Specific Example 



Preparation of a Wholemount op a Mite by the Method of Berlese 



The use of the name Berlese in the head- 

 ing of this example is less an injunction to 

 employ the mounting medium of that 

 writer than a tribute to the method of col- 

 lecting small arthropods which he intro- 

 duced. This method is applied with the aid 

 of the Berlese funnel which is seen in Fig. 

 21. This is a double-walled funnel, between 

 the walls of which warm water may be 

 placed and maintained at any desired 

 temperature by applying a small flame to 

 a projecting side arm. The temperature is 

 not critical, so that no thermostatic 

 mechanism is provided, but a thermom- 

 eter may be inserted and used to read the 

 temperature at intervals. A circle of wire 



gauze with a mesh of about K 6 of an inch 

 is placed at the bottom of the inner glass 

 funnel, and whatever material to be 

 searched for mites is placed loosely on this 

 gauze. The lower end of the glass funnel 

 is then attached with modeling clay to a 

 tube containing whatever medium is being 

 used for the collection of the specimens. 

 If the specimens are merely to be stored, 

 rather than mounted at once, 95% alcohol 

 may be placed in the tube, and it is then 

 unnecessary to seal it to the base of the 

 funnel. If, however, the specimens are to 

 be mounted directly in Berlese's medium, 

 in which better mounts can be prepared 

 from living than from preserved material, 



