Dehydration 



WHOLEMOUNTS IN RESINOUS MEDIA 



55 



rather than a useful, mount are recom- 

 mended to try the technique of Lynch 

 (Chapter 20, DS 13.7 Lynch 1930). 



Plant Materials. Plant specimens for 

 wholemounts often consist of only one, or 

 at the most two, layers of cells and are 

 easier to stain than zoological specimens. 

 The nuclei may be stained either with saf- 

 ranin (Chapter 20, DS 11.42) or with any 

 of the iron hematoxyUn techniques (Chap- 

 ter 20, DS 11.11) which in zoological 

 procedures are rigorously confined to sec- 



Dehydration is carried out by soak- 

 ing the specimen in gradually increasing 

 strengths of alcohol, it being conventional 

 to employ 30%, 50%, 70%, 90%, 95%, 

 and absolute alcohol. The writer prefers to 

 omit from this series, unless the object is 

 very deUcate, both the 30% and the 50% 

 steps in the process, thus starting with di- 

 rect transfer from water to 70% alcohol. 

 The only difficulty likely to be met in de- 

 hydration is in the handling of small speci- 

 mens, for if they are in specimen tubes it 



Fig. 23. Transferring objects between reagents with cloth-bottomed tubes. 



tions. A contrasting plasma stain may 

 be used after the nuclei have been well 

 differentiated. 



Dehydration 



It is to be presumed that the specimens, 

 plant or animal, stained or unstained, are 

 now accumulated either in distilled water 

 or in 70% alcohol according to the treat- 

 ment which they have had. It is now 

 necessary to remove the water from them 

 before they can be transferred .into a 

 resinous mounting medium. Ethanol is 

 widely used as a dehydrant and, at least 

 in the preparation of wholemounts, only 

 its nonavailabihty should make any sub- 

 stitute necessary. If substitution is neces- 

 sary, acetone or methanol, in that order of 

 preference, may be used, but they have 

 the disadvantage of being more volatile 

 than ethanol and, therefore, require more 

 care in handhng. 



is almost impossible to transfer them from 

 one to the other without carrying over too 

 much weak alcohol. The writer has long 

 since abandoned the use of tubes in favor 

 of the device seen in Fig. 23. This is a 

 short length of glass tube, open at both 

 ends, with a small piece of bolting silk or 

 other fine cloth tied across the lower end. 

 The specimens are placed in these httle 

 tubes which (see illustration) are trans- 

 ferred from one stender dish to another 

 wdth a minimum chance of contamination. 

 These tubes are commercially available in 

 England but in America must either be 

 imported or homemade. 



There is no means of judging when de- 

 hydration is complete save by attempting 

 to clear the object. It is unwise to beheve 

 the label on an open bottle or jar if it says 

 absolute alcohol because this reagent is hy- 

 groscopic and rapidly absorbs water from 

 the air. One should, therefore, keep a 



