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PEOGRESS OF MICROSCOPICAL SCIENCE. 
action is to be studied. If the parts to be studied do not require 
hardening, it is best to dissect them out immediately after death, 
glycerine being used to keep them transparent, for when preserved 
in glycerine the structures can be left to any convenient time for 
examination. When spirit is used, hardening occurs in a few days, 
after which the tissues shrink and become granulated and knotted 
together so as to break under dissecting needles ; besides which they 
gradually get stained and opaque, so that they are not any longer 
well seen under the microscope by transmitted light. Water should 
not be used when dissecting, but the object must be floated in 
glycerine, and all fatty tissues removed as soon as possible. 
The magnifying power under which dissection is carried on 
necessarily varies with the minuteness of the object — the lowest 
power under which the parts can be distinguished should always be 
chosen, because they can be kept better in sight and a firmer control 
over the movement of the dissecting needles exercised. With high 
power, the object escapes readily out of the field, and the needles are 
not easily brought to bear upon it. The power should be either a 
single lens, or a combination of lenses which magnifies without 
inverting the image. 
Most insect preparations can be examined and made under a low 
power (5 to 25), but it is well to examine them under higher power 
during their preparation (50 to 75). When histologic elements are 
studied, still higher powers are needed. If, for instance, insect 
muscle is the object to be examined, the striation may be readily 
seen with quite low powers, but the arrangement of sarcous elements 
can be demonstrated only when powers varying from 400 to 800 are 
used. And by far the most beautiful objects are obtained when 
polarized light is used and advantage taken of the different refracting 
power of the disks and intervening substance. The ordinary striation 
of muscle fibre may be seen most perfectly in the muscles of the 
thorax, which naturally split up into long fibres, offering excellent 
specimens for study (e. g., in the common house-fly). For minute 
analysis of the sarcous mass, the muscles of mites (Trombidium) have 
been recommended, as the striation of si ch muscles is remarkably 
coarse and distinct. 
Muscle must be taken from an insect immediately it is killed. It 
may sometimes be advantageously treated with alcohol, or osmic 
acid (weak solution) and prepared in glycerine. When studying 
the phenomena of contraction, which will be seen in various phases 
along the length of the fibre, the muscle should be examined either 
in living insects, or in recently removed parts immersed in blood 
serum or some albuminous fluid (white of egg, e. g.), or in glycerine, 
but never in water. In insect muscle preserved in spirit, especially 
if the insect has been dropped, while living, into the spirit, the 
varying state of contraction of different elements of the same fibre 
may be seen just as fixed at the time of death. 
It frequently happens that the anatomist has not the opportunity 
of dealing with insects in the living or fresh condition. In such 
cases the specimen must be preserved in weak alcohol. 
