tiie 
STRUCTURE.AND ACTION 
OF 
STRIATED MUSCULAR FIBRE. 
My TIIOMAS DWIGHT, .Jit., M.D.. 
Pltni'l.ssnK OK WATOMV \T THE MKHK \L SC HOOL or MAINE. THE 
STIUJCTURE AND ACTION 
OF 
STRIATED FIBRE. 
1>y TIIOMAS DWIGIIT, Jit., M.D.. 
lMtOFKSSOK or ANATOMA AT Till'. MEDK'Ar, Sniiml, OF MAINE. [From the Proceedings of the Boston Society of Natural History, Vol. xvi, 
November 6th, 1873.] 
STRUCTURE AND ACTION 
OF 
STRIATED MUSCULAR FIBRE. 
THOMAS DWIGHT, JR., M.D. 
It would be alike tedious and superfluous to attempt to recapitulate 
the various views held on this subject, not only because this has been 
repeatedly done, but also because most of the methods employed 
have been so unsatisfactory as to throw doubt on the conclusions. 
Fibres have been used after removal from the body, teased out by 
needles, or flattened by the covering glass, and further affected by 
the abnormal media (among which even air is to be reckoned) in 
which they were examined. The contractions occurring under these 
circumstances are irregular, and mostly short-lived. Another very 
important objection appears to have escaped attention, namely : that 
when a muscular fibre is removed from the body it has lost its at- 
tachments, and owing to its properties of tonicity and elasticity it 
must, either at rest or in action, be in different relations from those 
of the living fibre. Merkel1 states frankly that he never has been 
able to follow the steps of contraction. He could see the fibre begin 
to move, the movement become quicker, and then the contraction 
would be complete without his having been able to see the inter- 
mediate phenomena. He contrived to obtain permanent views of 
more or less contracted fibres by throwing small parts of living ani- 
mals into absolute alcohol, which struck the fibres dead in all the 
stages of vital action, but he has disregarded the chances of error 
from the specific action of the reagent on the substance of the fibres, 
1 Archiv far Mikroskopische Anatomie, Band vm, Heft 2. 4 
and on their last movements. Wagener and Engelmann appear to 
have made some observations on living animals, or on parts of them, 
but I have seen no detailed account of these studies, and cannot 
think that they carried them far, for had they done so they certainly 
would not have relinquished them. 
After studying fibres pulled from the legs of flies and grasshoppers, 
I turned my attention to water beetles, and accidentally discovered 
that the legs of several of the smaller kinds were sufficiently trans- 
parent to give a good view of the muscles in situ, but that the genus 
Gyrinus is far superior to any other. The method is very simple: 
a leg of either the middle or hind pair is cut off, between the coxa 
and trochanter if possible, and put on a slide in a drop of water un- 
der a very thin covering glass. Care should be taken to have the 
leg tolerably straight, for if much flexed some of the best parts are 
obscured. The muscles are here in an almost perfectly normal con- 
dition, for their attachments are uninjured, and the water in which 
the leg is placed (its native element, by the way) can hardly pene- 
trate beyond the joint below the point of division. The only disad- 
vantage is that the specimen is cut off' from its nutrient and nervous 
supplies. A successful experiment affords one of the most striking 
views in the range of microscopy; the muscular fibres of apparently 
semi-fluid consistency are in almost constant, though irregular, mo- 
tion, carrying the smaller branches of the trachiae to and fro, as 
seaweed is swung by a wave. These phenomena sometimes continue 
for an hour and a half, with no other encouragement than an occa- 
sional slight tap on the covering glass. The following observations 
have been made on the trochanter, the femur and the tibia. In the 
two former it is easier to find places where there is but one layer of 
fibres, but the tibia is usually preferable, for the shell is more trans- 
parent, and there are many fibres attached at different degrees of 
obliquity to a tendon, so as to illustrate the effect of more or less ten- 
sion. Moreover, these fibres, owing perhaps to the proximity of a 
large tracheal dilatation, preserve their irritability much longer than 
others. 
The work of which this paper contains the results, has been done 
entirely on preparations of this kind of the legs of the Gyrinus. 
The observations were made while the fibres were still capable of 
contraction. Hartnack’s immersion objectives, Nos. 9 and 10 (usually 
the latter) were employed, with his No. 3 ocular, and the draw-tube 
drawn out. 5 
As is well known, the muscular fibres of insects are not bound to- 
gether by interstitial tissue nearly so strongly as those of vertebrates, 
and each is able to contract freely independently of its neighbors. 
The states in which muscular fibre is seen may be divided into four 
chief ones. 
The first state (Plate n, fig. 1 and fig. 2, A) is the essentially nor- 
mal one in which the fibre is at rest, but extended between points 
far enough apart, and sufficiently fixed, to oppose a certain resistance 
to its elasticity and contractility. 
The second state (fig. 3) is seen when the fibre is free from all strain 
or resistance; it is that which a fibre in the first state would assume 
if one of its attachments were divided, or moved much nearer to the 
other. 
The third state (fig. 2, C), usually owing to contraction of another 
part, is one in which a part of a fibre is put upon a decided stretch. 
The fourth state (fig. 2, B) comprises all the degrees of active con- 
traction. 
In the first state the borders of the fibre are straight, and are con- 
nected by narrow transverse bands of a black granular structure, which 
present considerable variation. Usually the minute black granules lie 
so near together that no other substance is visible between them, but 
sometimes they are separated into two distinct lines in a transparent 
ground substance, and again they may be so close together as to give 
the band an almost homogeneous appearance. On each side of these 
bands is a glaring white one, usually broader on one side than on the 
other. As the stage is rotated the brighter band pales, and the dim- 
mer one brightens, while minute changes in the adjustment or illu- 
mination produce similar almost indescribable effects.1 The bright 
bands are connected by a broad gray stripe, which is midway be- 
tween two black bands. I have never seen a lighter stripe in the 
middle of the gray one in muscle inside the body, but can fully con- 
firm the common account of it in fibres pulled from the leg of the fly. 
To recapitulate; a fibre at rest consists of a series of gray stripes 
with white borders situated between black granular bands. 
The second state is best studied on fibres running to the lower part 
of the tendon that passes from the tibia to the end of the limb, for in 
many positions of the leg they are completely relaxed, and hang in 
graceful curves. When, as sometimes happens, the tendon is broken, 
they are seen to particular advantage. The whole fibre is broader 
t Vide Heppner in Archiv fur Mikroskopische Anatomie, Band y, Heft 1. 6 
than in the first state. The black bands are usually somewhat nar- 
rowed, and also drawn nearer together. Their granular nature can 
almost always be made out, but the granules are never seen in two 
rows. The white and gray stripes are both visible, but are narrower, 
especially the former, than in the normal condition. The edges of 
the fibre are scalloped. The ends of each projection come into the 
borders of the black bands, the greatest bulging being opposite to 
the middle of the gray. 
In the third, or stretched condition, the fibre is decidedly narrower, 
with a peculiarly sharply defined outline. The granular bands are 
pulled apart into two parallel lines of dots lying in a brilliant clear 
ground, which is continued into the two white bands. The gray 
band is lighter, and the bright bands darker than when at rest, so 
that all parts of the ground substance present nearly, though not 
quite, the same appearance.1 The appearances of contracted fibre 
will be best described in connection with the accompanying phe- 
nomena. 
On looking at the tibia or femur when the fibres are in active con- 
traction, the attention is constantly distracted by the strangeness of 
the view, and by the multiplicity and rapidity of the changes in pro- 
gress. It requires much practice and the closest attention, to fix the 
eye on a part of a fibre at rest, and to keep it there so as to note the 
successive changes. If the contraction be very rapid it is probably 
impossible to do so, but when it is becoming weaker it can be done 
very fairly; but I must admit that I have not been able to satisfy my- 
self positively on certain points to be presently noticed. This much, 
however, is certain, namely, that with experience it is easy to follow 
an individual black band from the state of rest to that of full con- 
traction, which shows that the homogeneous stage (Zwischensta- 
dium), supposed by Merkel to occur in partial contraction, has no 
existence, and that his theory of an exchange of places between two 
substances in closed cases is impossible. The general impression 
given by a wave of contraction is that a part of the fibre dilates, 
that the black bands become more prominent and, while approaching 
each other, run with the wave along the fibre. This last appearance 
is partly true and partly deceptive, for to be drawn together the 
bands must really move; but the effect is exaggerated by new parts 
in front of the wave, entering into contraction as those behind it are 
relaxed. The substance between the black bands is evidently the 
1 In fig. 2, C, the difference between the gray and white is too marked. 7 
contractile element. Two or three bands are seen to be drawn 
quickly nearer together, and the gray substance between them disap- 
pears, so that there is an alternation of black and white stripes. This 
first step of contraction occurs so rapidly that the observer is 
scarcely aware of it before it is completed, but as the wave runs 
along the fibre it is more easily observed. The black bands can be 
seen to approach one another, and sometimes even the granules com- 
posing them to get nearer together; in full contraction they are 
sometimes apparently homogeneous, sometimes granular, but it is 
important to notice that their edges are rarely sharply defined 
against the white; they appear irregular and granular. The borders 
of the fibre are so frequently seen to become scalloped, that I cannot 
but think it the universal law, though often, owing to the proximity 
of other fibres, the swellings cannot be seen. At the point of great- 
est contraction the fibre is much broader than elsewhere, and there 
is no doubt that the black bands are lengthened; nevertheless they 
appear longer than they really are, for the bulgings at the ends of the 
light bands come so near together that they almost touch one another, 
and their edges being rendered indistinct by optical effects appear, in 
part, as prolongations of the black bands. 
The most puzzling point of all is to decide at just what stage of 
contraction the gray disappears. This is particularly difficult to ob- 
serve, because the colors are changing their shades and positions at 
the same time. It is certain that the gray has disappeared somewhat 
early in the contraction — say in its first half, and also that it is not 
the very first change, for it may be seen in very slightly contracted 
fibres. There does not appear, at least in the detached leg, to be 
any law regulating the direction of the wave; it seems quite acci- 
dental whether it runs toward the tendon or from it. Usually it 
begins at one end of a fibre, and after a moment’s pause runs the 
whole length, when it either dies out, or, as is more frequently the 
case, returns, gradually growing weaker, and embracing less of the 
fibre. When the specimen is fresh and lively, a wave of average 
size comprises the substance between seven or eight bands, and as 
long as contraction lasts, rarely less than that of three elements is 
involved. As the wave runs toward the end of a fibre the part be- 
hind it is put more or less upon the stretch, frequently enough so for 
it to assume the condition already described as the third state. 
When the contraction is nearly over, it is not rare to see the fibre 
restored to its normal state by a sudden jerk in the direction opposite 8 
tp that pm-sued by the wave, evidently caused by the elasticity of 
the stretched portion. The contractile force of the part of fibre in 
action overcomes the elasticity of the part at rest, but at a certain 
moment the latter property reasserts itself. 
Merkel, as already mentioned, describes a homogeneous appearance 
as characteristic of a certain stage of contraction. Schafer, on 
the other hand, thinks it occurs during perfect rest. For my part I 
have never seen it at all. In beetles, however, that have suffered 
from confinement, it is not very rare to find the markings very indis- 
tinct, and in some cases many stray granules are found in the fibre, 
particularly near the surface. I have often noticed the latter appear- 
ance after the muscle had become exhausted by electricity. The 
long muscle corpuscles, well described and represented by Klein,1 are 
often seen very near the surface of the fibre. In the living and 
healthy muscle a longitudinal striation is almost never seen, though 
it appears in unhealthy fibres. It is superficial, and probably exists 
solely in the sarcolemma. 
The polariscope has been much used, in order to decide on the 
differences of the nature of certain parts, but the results of different 
observers are not in harmony, and it may well be questioned whether 
results obtained by its use on fibres hardened bv reagents, are of any 
particular value. In the case of the entire leg, it proved unavailable 
for the presence of two layers of shell, enclosing often more than one 
layer of muscle, rendered the few results which I obtained quite un- 
trustworthy. It has been stated that the staining qualities of hasma- 
toxylin make it a substitute for polarized light; accordingly I repeat 
edly put a living beetle into a pretty strong solution; but though I 
once left one in for twenty-four hours, during the greater part of 
which time life was extinct, the tissues showed that none of the col- 
oring matter had passed the skin, so that I was obliged unwillingly to 
give up this class of experiments. 
By the kindness of Professor Henry P. Bowditch, I was enabled 
to perform in his laboratory a series of electrical experiments with 
both the constant and the interrupted current. The effect of a sin- 
gle shock, or of the use for a short time (say a minute) of a weak 
interrupted current, was to produce lively, though irregular action; 
the waves ran in both directions simultaneously. If a strong inter- 
rupted current were used, or a weak one were long continued, the 
muscle became tetanized; the waves of contraction ceased, and 
1 Handbook for the Physiological Laboratory. 9 
whole fibres assumed the appearances of the extremest contraction 
throughout; nothing could be seen but a succession of very narrow 
black and white lines. The experiments with the constant current 
promised to be of great interest, but as they were very difficult, and 
threatened to lead me far beyond my original plan, I soon decided to 
leave them for abler hands. 
Let us now glance at the difference of the results obtained by this 
method, and by examining fibres taken from the legs of the large 
water beetles, Hydropliilus and Dytiseus. For the appearances of 
of the Hydropliilus, I have used Ileppner’s plates (loc. cit.), 
and for those of the Dytiseus, original observations on fibres from the 
leg without any reagent. The muscles of the two are precisely simi- 
lar. By comparison with those of the little Gyrinus, in situ, it ap- 
peared that the fibres of the larger beetles were much broader, but 
that the stripes were in proportion much nearer together. To see if 
this did not depend on the abnormal condition of the larger fibres, I 
endeavored to obtain fibres from the Gyrinus. There was little diffi- 
culty in doing this if a leg, or a part of the abdomen, were broken to 
pieces in a drop of fluid, but unfortunately it was almost impossible 
to separate the muscles from the shell without such addition, and 
when a minute piece was fortunately isolated, it, as a rule, immedi- 
ately became dry and useless. Fig. 4, PI. n., represents a fibre teased 
out in glycerine; it shows that the black stripes are strongly drawn 
together, that their granular structure is indistinct, and that the gray 
bands are wanting. It is more or less obscured by the longitudinal 
folds of the sarcolemma which give it a somewhat fibrillated appear- 
ance. The particular fibre chosen is not an extreme case; on the 
contrary, most fibres were much more obscure, and those in water 
more contracted than those in glycerine. In the few specimens of 
any value to which no fluid had been added, most of the fibres were 
less normal than the one drawn, and I can remember but two indi- 
vidual fibres that were decidedly more so. There can be little doubt 
that if it were possible to examine the fibres of the larger water 
beetles, in situ, that they would present quite different proportions 
from those usually ascribed to them. 
The following are briefly the conclusions which the preceding ob- 
servations appear to warrant. The fibre consists of a sheath, the 
sarcolemma, and of a ground substance, in which elements which 
may provisionally be called granules, are imbedded in transverse 
double rows. There is no reason to suppose that the difference be- 10 
tween the white and the gray has any other than an optical cause, 
namely: that the part of the ground substance nearest the black 
bands receives not only the rays of light that would naturally strike 
it, but others reflected or refracted, or both, from the black bands, 
and which do not strike the middle of the space between the latter. 
(Heppner.Schafer.) If this be admitted, it is merely a corollary 
that, in contraction, the gray should disappear; as is the case. No 
appearances have been seen that are suggestive of the handles of 
Schafer’s dumbbell-like rods, which, indeed (judging from the abstract 
of his paper), he has assumed rather than demonstrated. As has 
been already stated, nothing like fibrillar structure is to be seen in 
the living and healthy fibre. 
The sarcolemma is firmly attached to each edge of the ends of the 
black bands, and the granules must, in some way, be prevented from 
separating laterally, so as to give the support for the folds, into which 
the muscle contracts. The ground substance is the contractile ele- 
ment; it is also highly elastic. When the fibre is stretched all parts 
become narrower, and when contracted, broader; but in the latter 
case the change is chiefly in the ground substance. 
EXPLANATION OF PLATE 2. 
The drawings are all from fibres of the Gyrinus, as seen with objective 10 im- 
mersion, and No. 3 eyepiece (Hartnack), and are slightly reduced. 
Fig. 1. Muscular fibre at rest under normal conditions, showing the various 
appearances of the granular and bright bands. 
Fig. 2. A fibre at rest at A, contracted at B, and stretched at C. 
Fig. 3. A fibre in passive contraction (second state) attached to a tendon. 
Fig. 4. A fibre teased out in glycerine. 
The drawings are more or less diagramatic, owing to the great difficulties which 
the object presents. This is particularly the case at B, in fig. 2, and can easily be 
accounted for when it is remembered that the wave of contraction is never sta- 
tionary for a second. The gray at C, in fig. 2, is too dark. Proc. Bost. Soc. Nat. Hitt. Vol. XVI. 
Plate 2. 
Dr. H. P. Quinct, Del. 
Heliotype. 
DWIGHT, STRUCTURE OF MUSCULAR FIBRE.