113 Mr. W. M. Dobie on the Minute Sti^cture 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 outhne 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 fibrillse in a transverse 

 direction, and giving the light spaces as now seen a rectangular 

 figure." (Fig. 3 a b.) 



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. 4«&6). 



Dr. Carpenter examining the same dissections comes to a 

 similar conclusion (fig. 2 b). 



Professor Allen Thomson of Glasgow, in his late work on Phy- 

 siology, describes the structure of the fibrillse in the same way as 

 Dr. Sharpey : but since the pubhcation of that work he has been 

 led to doubt the existence of any lateral clear edge, as he himself 

 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 fibrillse 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 fibrillse, 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 fibrillse 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 fibrillse 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 fibrillse 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 



