MOVEMENTS OF VOLUNTARY MUSCLE. 
471 
Having endeavoured to prove the nature of the transverse striae, and the general 
construction of the fasciculi, I next proceed to inquire more particularly into the 
nature and form of the minute segments of the fasciculus already spoken of. In 
doine- this, it will be the most convenient to consider them as they appear when 
united into fibrillae, this being the form under which they commonly present them- 
selves, and under which it has been customary to regard them. Many attempts have 
been made to ascertain their nature, but as it appears to me without sufficiently at- 
tending to the following circumstance ; That in consequence of the original and close 
union between contiguous fibrillae, not one can be separated from the mass without 
suffering an unnatural mutilation of some parts of its surface ; a mutilation which 
may have an influence on the form it may seem to possess. This source of ambiguity 
is such as to dispose me to receive with considerable hesitation the representations of 
primitive fibrillae furnished by authors ; and the few observations which here follow 
on this subject are offered with great diffidence. Muller describes the fibrillae as pre- 
senting “ a regular succession of bead-like enlargements, which are somewhat darker 
than the very short constrictions which intervene between them* *.” Dr. Schwann, 
as quoted by the same eminent physiologist, gives a similar account, while Mr. Skey 
considers the “ light to be the elevated striae, and the dark intervening lines the 
depressions but with respect to the relative width of the dark and light spaces and 
striae, it seems to be agreed that the dark are the narrower. In my examination 
of the several parts, I have been led to imagine a fallacy to lie in supposing any ab- 
solute diversity in their colour. They appear to be rather an effect of a difference in 
form, or probably sometimes in density alone, between the alternate points of the 
fibrillae. There does not seem to be anything in their appearance at variance with 
such a supposition, since if a rod of glass formed out of beads be held to the light, 
the beads are distinguished by dark circumferences, and by broad dark bands be- 
tween them, which will vary with the inclination of their surfaces and the length of 
the intervening spaces, and would besides be much assisted if the connecting portions 
were of a less refractive material. Moreover, if two such rods be placed in contact, 
bead to bead, one behind the other, and then regarded between the observer and the 
light, the dark circumferences of the beads, at the margin of the rod, will be found to 
have vanished, the intervening bands being reduced to transverse lines or septa, or, 
in a word, the elements of striae. I have had an instrument of this sort constructed, 
which may be regarded as a very imperfect model of a primitive fasciculus, and which 
which may be called the component parts of a muscular fibre ; and I am apt to suppose that a change takes place 
in the position of those parts during contraction, and this alteration diminishes the extent of those parts in one 
direction, while it is increasing them in another, although from the experiments it appears not to be in the 
same proportion ; but what that attraction is, I shall not pretend to determine.” — Croonian Lecture on Mus- 
cular Motion, No. V., year 1781. Hunter’s Works, Palmer’s Edition, vol. iv. p. 261. 
* Physiology, translated by Balt, p. 879. 
