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disadvantages I therefore made some experiments in order to find a 
better solvent. After a little consideration I came to the conclusion 
that paraffin of low boiling point would probably dissolve the paraffin 
in which the sections are imbedded more quickly than the gutta percha 
film to which they are attached. This proved to be the case to a cer- 
tain extent; the gutta percha was however appreciably soluble. I 
therefore tried a solution of raw Caoutchouch (India rubber) in ben- 
zene instead of gutta percha with perfectly satisfactory results. 
Description of method. 
A thin solution of Caoutchouch in benzene or chloroform is 
prepared and poured over the slide so as to form a film in the same way 
that collodium is poured on a photographic plate. When the film is dry 
the sections are arranged on it, and the temperature of the slide raised to 
the melting point of the paraffin; the sections then fall on to the india 
rubber film which has become sufficiently sticky to adhere to them 
perfectly. When the slide is cold it is treated with naphtha or any 
light paraffin oil, the solvent action being more rapid the lower the boi- 
ling point of the oil used. Absolute alcohol is readily miscible with the 
naphtha or light paraffin so that the solvent is readily removed. ‘The 
slide can now be placed in successive alcohols, stained and returned 
to absolute alcohol. It is now to be cleared with kreosote or oil of 
cloves and mounted in the ordinary way. Apart from the great advan- 
tage of being able to stain on the slide thisindia rubber method seems 
to possess some points of superiority over the shellac method of Gies- 
brecht, Zool. Anzeiger 1881. This depends on the fact that Sec - 
tionscanbe mounted in balsam direct formthe naphtha. 
The following are some of the advantages over Giesbrecht’s method. 
1) The india rubber is more uniform and therefore safer for small 
objects. 
2) The indian rubber is dry and thus allows a more minute arran- 
gement of the sections on the slide. 
3) The naphtha solves the solid paraffin quicker than turpentine 
does. 
4) No traces of india rubber are visible after mounting since india 
rubber becomes perfectly transparent in balsam. 
These methods have been put to a rigorous test by Mr. Cald- 
well and are now in use in the Morphological Laboratory of this Uni- 
versity. 
Cambridge, March 28th 1883. 
