THE MUSC1 LAB SYSTEM. 281 



stria 1 , vary also; so that tlic fibrils which exhibit the most 

 distinct striation, arc almost as thick again as the others, and 

 their transverse striic are placed almost twice as closely to- 

 gether. It may thence, perhaps, be allowable to conclude, that 

 in the act of contraction the principal phenomenon consists 

 in the shortening and thickening of the fibrils, and also, that 

 the changes in the fasciculus above noticed depend upon these 

 changes in the fibrils. The further question now arises : how 

 is this shortening of the fibrils effected ? and whence does the 

 transverse striation arise? Is the latter connected with the 

 vital conditions of the muscle, or is it produced independently 

 of these ? It is unnecessary to answer the latter query in 

 the affirmative, for dead muscles exhibit transverse striae, and 

 indeed, under the same conditions as the living. This is best 

 shown in muscles successively subjected to various degrees of 

 tension ; and consequently, all notion of a merely partial con- 

 traction of the fibril, which arises on the first observation of 

 these conditions, must be relinquished. The transverse stria- 

 tion is manifestly merely a physical, not a vital phenomenon. 

 It arises, either because the fibrils are not homogeneous through- 

 out their whole length, but divided into numerous small seg- 

 ments, some of which are possessed of greater elasticity than 

 the others ; or, in the opposite case, it may depend upon the 

 circumstance, that the fibrils are soft filaments, which, in shorten- 

 ing, become curved in a zigzag or wavy manner, or varicose. 

 Which of these two views is the correct one, cannot at present 

 be determined; and this much only can be said, that in favour 

 of the former supposition, the fact can be adduced, that fibrils, 

 after maceration, readily break up into minute particles (sar- 

 cous elements, Bowman), and possibly consist of a series of such 

 elements connected by a heterogeneous interstitial substance ; 

 whilst in favour of the second, are the conditions presented in 

 the fibrils of connective tissue, which are undoubtedly homo- 

 geneous throughout, and yet when made to contract by the 

 application of acetic acid, exhibit extremely delicate trans- 

 verse markings, in consequence of which, the fasciculi composed 

 of them frequently offer a deceptive resemblance to those of 

 striped muscle. It is difficult to say whether the sarcolemma 

 participates actively in the shortening of the fibrils, although, 

 especially from the consideration of its chemical and physical 



