Bauhaus-Universität Weimar

Titel:
Handbook for the Physiological Laboratory. Text
Person:
Burdon-Sanderson, John Scott E. Klein Michael Foster T. Lauder Brunton
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit18583/64/
BY DR. KLEIN. 
55 
slightly pressed, so as to flatten out the object, arborescent 
branchings of the tracheæ first attract attention. These air- 
tubes consist, like the tracheæ of mammalia, of parallel rings, 
and entwine the muscular fibres with a network of fine, dark 
capillaries, each of which follows a winding or spiral course. 
The muscular fibres themselves, which either run parallel, or 
cross each other in various directions, are in active movement. 
In some fibres this movement resembles that of a wave, which 
rapidly progresses in the direction of its length ; in others, when 
it is slower, it has a vermicular character. On more careful examina¬ 
tion it is seen that, during the progress of the wave, the muscle 
swells, returning to its original thickness immediately after. It is 
further observed that the dark parallel striæ come nearer together 
during the swelling, and that the intervals return to their original 
width after the wave has passed. In the contents of amuscular fibre, 
when in a state of rest, the following parts can be distinguished : 
(a) the dark, parallel cross stripes, which, as we shall find, 
correspond to thin parallel disks of less refractive isotropous 
substance (called interstitial disks) ; (b) the portion intervening 
between these. This, again, appears to consist of two parts, viz., 
a broader middle one of dull grey appearance, and on either side 
of this a narrow, clear layer. The whole is made up of highly 
refractive, anisotropous, contractile substance, which is to be 
regarded as the essential substance of the muscular fibre. The 
dark cross-lines do not seem, under high powers, homogeneous, 
but appear to consist of series of contiguous granules of equal size. 
Many muscular fibres exhibit no other differences; in others, it is 
possible to distinguish lines running longitudinally, of greater 
or less extent, and which are so arranged that they come be¬ 
tween what appear to be dark granules of the interstitial striæ. 
With reference to these granules, it is not to be supposed that 
they actually exist as such ; the appearance is rather to be 
regarded as expressive of the fact that the dark, interstitial 
transverse stripes are interrupted by clear, longitudinal lines, the 
interval between the latter remaining dark—as, e.g.y in a check 
of which dark transverse lines are covered by light longitudinal 
lines. In a fresh muscular fibre, as seen under the microscope, 
the transverse interstitial disks are not placed vertically, as we 
can satisfy ourselves by using the fine adjustment, but are set at 
an oblique angle with the long axis of the muscular fibre. In 
this respect a muscular fibre may be compared to a roll formed 
of coins of different metals, so arranged that the thin dark disks 
alternate with thicker light ones. If such a roll is laid on a 
plain surface, all the coins lean in one direction, and present 
their edges to the eye, regarding them from above, just as the 
disks in a muscular fibre do under the microscope.
        

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