260 SPECIAL HISTOLOGY. 



fibrils which exhibit the most distinct striation, are almost as thick again 

 as the others, and their transverse striae are placed almost twice 

 as closely together. It may thence, perhaps, be allowable to con- 

 clude, that in the act of contraction the principal phenomenon con- 

 sists 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 con- 

 sequently, all notion of a merely partial contraction of the fibril, which 

 arises on the first observation of these conditions, must be relinquished. 

 The transverse striation is manifestly merely a physical, not a vital 

 phenomenon. It arises, either because the fibrils are not homogeneous 

 throughout 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 shortening, become curved in a zig- 

 zag 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 favor of the former supposition, the fact can be adduced, 

 that fibrils, after maceration, readily break up into minute particles 

 (sarcous elements, Bowman), and possibly consist of a series of such 

 elements connected by a heterogeneous interstitial substance ; whilst in 

 favor of the second, are the conditions presented in the fibrils of con- 

 nective tissue, which are undoubtedly homogeneous throughout, and yet 

 when made to contract by the application of acetic acid, exhibit extreme- 

 ly delicate transverse 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 partici- 

 pates actively in the shortening of the fibrils, although, especially from 

 the consideration of its chemical and physical properties, which ap- 

 proach those of elastic tissue, I am rather inclined to the opinion, that 

 its function, in the contraction of the fibre, is merely passive. The 

 same may with greater certainty be affirmed of the albuminous fluid 

 uniting the individual fibrils. Consequently, it is not the muscular 

 fasciculus, in toto, but only the fibrils, which are to be regarded as the 

 contractile elements ; a position which is not shaken by the circum- 

 stance, that other conditions occur in the smooth muscles, and in many 

 muscles in the Invertebrata (those that exhibit no fibrils). 



This is not the place to dilate upon the causes to which the contrac- 



