OF MICROSCOPIC OBJECTS, 21 
any amount of soaking to render them sufficiently trans- 
parent, some bleaching process should be premised. A for- 
mula for such a process may be found in another part of 
this work, where the preparation of the antennz of insects 
is described. If that should not prove successful, some 
modification will easily occur to the student. Of course it 
is not all insects that can be treated in this way, the size 
and deep colour of very many quite preventing a good 
result; but when they have been successfully prepared by 
any of the methods of which we have spoken, it is then 
possible to discriminate their internal organs by the differ- 
ences of colour which they present. The use of the binocular 
microscope, and of objectives of low angular aperture, will 
also much facilitate this mode of examination, by increasing 
the depth of focus, and enabling the organs to be seen more 
or less in connection with each other, even if they be super- 
posed. It is also possible to examine the muscles of the 
limbs and bodies of insects, so as to decide upon their forma- 
tion, origin, and insertion, and probable mode of action; and 
this is only one of many such uses. What a mistake must 
it be, then, to prepare insects for mounting’ by boiling in 
liquor potasse, and so dissolving out their viscera, and 
squeezing them flat! 
In the case of living insects, especially those of the more 
transparent salt and fresh water species, the results of their 
- examination by polarized light are exquisitely beautiful and 
interesting, because their organs and circulation may be 
more clearly discriminated while in motion. 
10TH DIvisIon. 
Electricity has been employed in histology partly for its 
electrolytic effects, but chiefly as a means of producing 
certain variations of temperature in objects under examina- 
tion. Stricker says “that the tissues become altered by it 
as they would be were they subjected to the action of weak 
acids or alkalias,” and he describes a rather complicated 
apparatus for this purpose, of which it is impossible to give 
