112 Mr. W. M. Dobie on the Minute Structure and ~ 
part is a little out of focus. The light parts are the centres of 
highly refracting particles acting as lenses; the dark points the 
intervals between them. If now the focus be carefully adjusted 
and the achromatic condenser be used for the purpose of defining 
the outline with the utmost precision, each dark interspace be- 
tween the refracting points will be found to be reduced to two 
very slender straight lines, crossing the fibrille in a transverse 
direction, and giving the light spaces as now seen a rectangular 
figure.” (Fig. 3a 0.) 
Dr. Sharpey, from an examination of Mr. Lealand’s prepara- 
tions of the muscle of pig, considers the_sarcal particles each to 
be composed of a dark central and clear outer part. Dr. Sharpey 
mentions that Mr. Lealand himself first pointed out a cross line 
in the clear interval, and also the bright surrounding areas 
(fig. 4a & 5). 
Dr. Carpenter examining the same dissections comes to a 
similar conclusion (fig. 2 0). . 
Professor Allen Thomson of Glasgow, in his late work on Phy- 
siology, describes the structure of the fibrille in the same way as 
Dr. Sharpey : but since the publication of that work he has been 
led to doubt the existence of any lateral clear edge, as he himse 
has informed me. 
’ Mr. Erasmus Wilson, from an examination of Mr. Lealand’s 
preparations, which he is pleased to call his “own. investiga- 
tions,” describes the fibrillze very differently ; he does not repre- 
sent any clear lateral edge to the fibril ; he considers the clear as 
well as the dark space to be severally composed of a pair of cells, 
the dark pair containing a denser ‘ myoline”’ than the clear pair ; 
each of these cells is again subdivided into two, thus giving four 
square cells of equal size in each dark or light interval (fig. 5 
a & b). 
I shall now advert to my own views regarding this structure, 
which I have deduced from the examination of very numerous 
demonstrations of the fibrillze, which I have succeeded in making 
in several kinds of muscular fibre, generally in the perfectly fresh 
state. 
When a favourable specimen of the muscular fibrille of the 
frog, pig, or ox, is placed under a microscope magnifying about 
500 diameters, and.the focus is adjusted with great care to the 
point at which the fibrille can be seen with the greatest di- 
stinctness, or at what I shall term the distinct focus, the ap- 
pearance presented is the following :—The fibrille are seen 
to be divided equally into a series of quadrangular spaces or 
areas, which are observed to be of two kinds, the one dark, the — 
other clear or light, regularly alternating with each other. The 
