MAKING WHOLEMOUNTS 45 



over too much weak alcohol. The author has long since abandoned tubes in 

 favor of the device seen in Fig. 9. This is a short length of glass tube, open at 

 both ends, which has a small piece of bolting silk or other fine cloth tied 

 across the lower end. The specimens are placed in the tubes which, as may be 

 seen in the illustration, are transferred from one stender dish to another with 

 a minimum chance of contamination. These tubes are commercially available 

 in England, but in America must be imported or homemade. 



There is no means of judging when dehydration is complete save to attempt 

 to clear the object. It is unwise to believe the label on an open bottle or jar 

 if it says "absolute alcohol" because this reagent is hygroscopic and rapidly 

 absorbs water in the air. Therefore, one should keep a quantity of anhydrous 

 copper sulfate at the bottom of the absolute-alcohol bottle and cease to regard 

 the alcohol as absolute when the salt starts turning from white to blue. More 

 wholemounts are ruined by being imperfectly dehydrated than by any other 

 method. Even the smallest specimen should have at least 24 hours in absolute 

 alcohol before any attempt is made to clear it. 



Choice of a Clearing Agent. A clearing agent must be some substance 

 which is miscible both with absolute alcohol and with the resinous medium 

 which has been selected for mounting. The ideal substances for this purpose 

 are essential oils. They impart just as much transparency to the specimen as 

 does the resin used for mounting, so that one has, as it were, a preview of the 

 finished specimen. The use of benzene, which is recommended for preparation 

 of paraffin sections, has started to spread into the preparation of wholemounts. 

 In the author's opinion, it is utterly worthless for this purpose. It has a rela- 

 tively low index of refraction, so that one cannot tell, if one endeavors to use 

 it, whether or not the slight cloudiness of the specimen is due to imperfect 

 dehydration until after the specimen has been mounted in balsam. 



The first choice is terpineol ("synthetic oil of lilac") which has advantages 

 possessed by no other oil. It is readily miscible with 90 per cent alcohol, so 

 that it will remove from the specimen any traces of water which may remain 

 in it through faulty dehydration, and it does not make specimens brittle. It 

 also has a very slight and rather pleasant odor. Clove oil is the most widely 

 recommended essential oil for the preparation of wholemounts. It has only 

 two disadvantages: its violent odor and the fact that objects placed in it are 

 rendered brittle. If a small arthropod is cleared in clove oil, it is almost 

 impossible to get the animal into a wholemount without breaking off some 

 appendages. Clove oil, however, is miscible with 90 per cent alcohol. 



Mounting Specimens in Balsam. Nothing is easier than to mount a spec- 

 imen in balsam, provided that it has been perfectly dehydrated and cleared. 



