PREPARATION AND STAINING OF ODONTOPHORES. 
273 
AVheii satisfactorily arranged, breathe upon a clean cover-glass and 
place it upon the object -without enclosing air-bubbles, and then, while 
carefully avoiding moving the glass cover, wipe off the superfluous 
glycerine with a soft rag, and with a tine brush dipped in quick- 
drying gold size run a connecting line round the glass cover and slide 
and lay aside for a day or two to dry, before finishing off with cement. 
If Glycerine Jelly be preferred as the mounting medium, the bottle 
containing the jelly should be placed iu a cup of hot water until 
li(iuefied, and when the radula and jaw are satisfactorily arranged on 
the slide, place a cover-glass over them, and secure it by a clip, before 
running the now fluid jelly beneath the cover, under which it will 
(juickly penetrate by capillary attraction ; when thoroughly permeated, 
boil for a moment to get rid of vacuoles or vapour bubbles, and i)lace 
the slide aside in a cool place for two or three weeks; the superfluous 
jelly can then be removed and the mount completed with a ring of 
brown cement and a finishing coat of gold size. The objection to the 
use of glycerine is its h3^gi-oscopic nature, and in some districts the 
injurious effects resulting from this (quality can scarcely be securely 
guarded against by the most careful ringing. 
Canada Balsam is also used as a mounting medium when it is 
intended to stain the radula or where it is desired to use the polari- 
scope in the examination of the prepai’ations, and though the Balsam, 
in course of time, renders the teeth very transparent, that is no real 
obstacle to the successful use of the polai'izing apparatus. 
Staining, in the opinion of many microscopists, greatly facilitates 
the study of the more minute odontophores, a well-stained preparation 
showing the teeth as though formed of coloured glass or crystal. 
Although many stains are used bj' microscopists, the Eosin-Haima- 
to.xylin })rocess, as practised by Mr. E. W. W. Bowell, being practically 
permanent and so excellent in many ways, may be selected as a 
representative one. 
In this process, the ladula, after the final washing previously 
described, is wanned in water slightly acidulated with acetic acid to 
neutralize any trace of alkali left in the preparation ; it is then dehyd- 
rated with absolute alcohol, placed upon a clean excavated slide, and 
Ehrlich’s undiluted Hpematoxylin applied for two or three minutes ; 
should the blue stain, after its development by washing in tap water, 
prove to be too strong, the fault is (quickly corrected by a momentary 
sojourn in alcohol or water faintly acidulated by Hydrochloric Acid. 
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