Spiral Structure of Mtiscle. 87 



be in at the time of manipulation, while relaxation in the same 

 proportion causes the giving way in a longitudinal direction ; 

 and he offers the following as perhaps sufficient to account for 

 the difference. In contraction, where the transverse striae are 

 narrow, the spii-als cross each other (i. e. antagonize each other) 

 at the acutest angles ; and in such a state of course it is that 

 there occurs most easily a mutual cutting through, producing the 

 "discs" of Bowman, to be again referred to. On the other 

 hand, in relaxation the spirals meet only at obtuse angles, whereby 

 the tendency to cutting through is in proportion lessened. The 

 cutting through of the spirals when crossing at acute angles is 

 illustrated by reference to a play with twine, familiar to school- 

 boys. 



In the early stages of development, however, fasciculi are 

 sometimes met with in which the fibrillse are so surrounded with 

 large spirals, that longitudinal cleavage would be difficult how- 

 ever complete the relaxation. Of such large spirals, not merely 

 two, but many interlace, — each surrounding its own cluster 

 of fibrils. These large spirals pass into membrane and form 

 septa*. Now within the winds of the larger spirals there arise 

 smaller ones, which in their turn enlarge and pass into mem- 

 brane, to be succeeded by another generation, and so on ; by 

 which it is easy to understand the prevention of longitudinal 

 cleavage, as well indeed as the difficulty constantly met with 

 when endeavoiu'ing to obtain separate fibrUs for microscopic 

 examination. Again, the state of the primitive fasciculus in 

 fig. 7 was met with ; where the fibrillse, e, were shared by more 

 than one surrounding spiral, b ; the whole being surrounded by 

 a larger spii-al, a. Here also cleavage in a longitudinal direction 

 would be very difficult. Further, the author saw states in which 

 there was absolutely no cleavage, the fasciculus before breaking 

 off becoming tapered to a point, fig. 8. This tapering to a point 

 seemed referrible pai-tly to great distensibility ofthesarcolemma, 

 and partly to a loose condition of fibrils already somewhat re- 

 laxed ; and it is beautifully demonstrative of a spiral structure. 

 (See the figure, and contrast the direction of the curves of the 

 spirals at a with that at b.) Besides, at a the fasciculus was 

 thick, while at b it was thin ; and as the spirals became more 

 and more drawn out, the fasciculus became more and moi-e thin, 

 until it terminated in a point. (The arrow shows the longitu- 

 dinal direction of the fasciculus.) 



It not rarely happens in the breaking off of twine, in which 

 the two threads composing it arc of unequal extensibility, that 



* Bowman observed that the inner surface of the sarcolemma often [)re- 

 sented irrej^larities, which the author thiuks were no other than remains 

 of septa such as those above mentioned. 



