CAUSE OF STRIATION OF VOLUNTARY MUSCULAR TISSUE. 313 
some ten or twelve different parts. We may postpone, I think, 
indefinitely the consideration of these details. 
While there is great unity as to the appearance of a fibre 
during a state of rest, the changes which the fibre undergoes 
when passing into the contracted condition are not at all under- 
stood. Not only does one fail to find among histologists agree- 
ment as to the changes in appearance, but the interpretations of 
these are as numerous as the investigators themselves. All are 
agreed that, during contraction, the fibre asa whole shortens and 
thickens, but the changes in form which the cross strize undergo 
are not understood so well. 
Klein, in his ‘ Atlas of Histology,’ maintains the broadening 
of both stripes transversely, the dark stripe becoming thinner in 
the long axis, and the bright stripe more opaque. Ranvier 
(‘Traité Technique d’Histologie,’ p. 459) states that the only 
points one can conscientiously observe in the contraction of a 
living fibre are, that a knot or bulging forms, in which the dark 
bands approximate, being only separated by Dobie’s line. This 
led him to believe that the dark bands are the true contracting 
part of the fibre. Ranvier worked especially with osmic acid, 
fixing the fibres when at rest and during contraction. W. 
Krause (‘ Allgemeine und Mikroscopische Anatomie,’ p. 92) 
describes the contraction as follows:—The thickness (in the 
length of the fibre) of the dark stripe or an isotropous substance 
remains the same as far as can be seen, while the thickness of 
the isotropous substance “ Zwischensubstanz’’ becomes less. 
From this he argues that the substance of the clear stripe, which 
he considers as fluid “ Muskelkistchenfliissigkeit,” passes between 
the little elements of the dark stripe, causing their lateral sepa- 
ration, and therefore broadening and shortening the fibre. Hn- 
gelmann (“Neue Untersuchungen iiber die Microskopischen 
Vorgiinge bei der Muskelcontraction,” in ‘ Pfluger’s Archiv,’ 
Band xviii) is certain that the light stripe durig complete 
contraction becomes darker than the dark stripe, and that there 
is a period, as naturally follows from this observation, when 
the fibre is quite unstriated. The stripes are, in fact, reversed, 
the bright one becoming the darker, and vice versd. Both 
stripes narrow, but especially the bright one. Engelmann ad- 
vances a theory to account for this, holding that the cause of 
contraction is the passage of fluid from the isotropous clear - 
stripe into the anisotropous substance; the former shrinks and 
the latter swells. Most startling is the view of Merkel (‘ Hof- 
mann und Schwalbe,’ vol. i, p. 116), who believes that the dark 
stripe shifts its position, arranging itself by Dobie’s line, while 
the light stripe passes to the centre. 
It is, as will readily be admitted, somewhat difficult to know 
VOL, XXI,—NEW SER. x 
