of the Contractile Substance of the Polythalamia. 355 
contractile muscular fibre on its transition from the state of rest 
to that of action, and the reverse, is still very obscure ; there is 
even controversy upon its minute structure. Still an attempt to 
compare the two different forms of contractile substance at pre- 
seut known with each other appears justified, so long as only 
recognized and undoubted facts are brought into comparison, 
and thus new aspects and some progress, although but slight, 
may be made towards the further explanation of the contracting- 
power of the two structures. 
The following are the properties of muscular fibrewhich should 
be prominently brought into comparison :— 
1. The contractile particles of the muscular fibres are arranged 
with special regard to the long axis ofa cylinder or to some kind 
of longitudinal axis: every muscle consists of an aggregation of 
these longitudinally arranged contractile morphological ele- 
ments. 
2. No other means of recognizing the organism of the muscular 
fibres as a whole are known, except those which refer to the 
contractile power. 
3. The contractile action is accompanied by changes in the 
form of the muscular fibres, which I have designated active 
motory phenomena. The passive motory phenomena are exhibited 
in the neighbourhood of the contractile substance by displace- 
ment of the substance situated there, and any so-called passive 
sources of motion of the organisms which may be present—by 
conversion of the original pressing force of the shortened muscu- 
lar fibre into tractive force, &c. 
4. In regard to the active phenomena of motion, the following 
facts are established :— 
a. On the transition of the contractile substance of the 
muscular fibre into the so-called active or contracted state, it 
diminishes in longitudinal and increases in transverse section, 
either without or with but little change of volume. Or this may 
be expressed thus:—The slender elongated body is finally 
changed into a more or less thick plate or disk. On return to 
the state of rest, the original elongated form is restored. 
b. The shortening and thickening on the one hand, as also 
the elongation and diminution of breadth on the other, may 
apparently occur suddenly in the entire muscular fibre; they 
may, however, run as a contraction-wave, distinctly perceptible 
under the microscope, from one end to the other. 
c. The contraction may be limited to or localized in any seg- 
ment of the length of the muscular fibre. 
d. The contraction may stop at any intermediate state within 
the most. extreme limits; it may then either increase or pass 
from the state of action to that of rest. 
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