298 VARIATIONS OF STRUCTURE IN DIFFERENT MUSCLES. 



upon the following series of researches into the structure of muscle. Various observers 

 (Melland, Gr. F. Marshall, van Gehuchten and Ramon y Cajal), who during the next five or 

 six years investigated the structure of muscle, mainly with the aid of acid and gold prepara- 

 tions, have regarded the appearances of these preparations as proving the existence of a similar 

 reticulum in muscle, and have concluded that the material in the meshes of the supposed 

 reticulum, that is to say the whole of the muscle-columns, must represent the enchylema of 

 protoplasm. The breaking up of the so-called inter-reticular substance into muscle-columns 

 is regarded as purely artificial. 



Although the above view of muscle-structure obtained for a short time some adherence 

 amongst histologists, and has not even at the present time been given up by all its original 

 supporters, it must certainly be relinquished as being inconsistent with the known facts of 

 muscle-structure. The researches of Rollett, which were published in 1885 and 1886, showed 

 any such view to be untenable, and brought the matter back to the former standpoint. The 

 results of these researches tended to demonstrate that the filaments of the so-called " reti- 

 culum " of the above-mentioned authors are neither more nor less than the septa of sarcoplasm 

 which intervenes between columns of the muscle-substance : that these columns pre-exist in 

 muscle, and are the actual contractile elements of the muscle ; and that the sarcoplasm between 

 them is a passive material, and may represent the undifferentiated remains of the protoplasm 

 of the original cell from which the muscular fibre has been developed. 



The account in the text is derived from a re-investigation of the structure of muscle, 

 and especially of the muscles of insects, prepared by various methods and photographed with 

 the aid of Zeiss' 2 mm. homogeneous apochromatic objective. It differs materially from that 

 in the last edition of this work, which was based mainly upon investigation of living muscular 

 tissue only. The description of the actual appearances of living muscle still however stands- 

 good, and has been retained in this edition. 



Muscle-nuclei (muscle-corpuscles). In connection with the cross-striated 

 substance a number of clear oval nuclei are found in the fibres. In mammalian 

 muscles they lie mostly upon the inner surface of the sarcolemma (figs. 326, 330, A) r 

 but in frogs they are distributed through the substance of the fibre, and in many 

 insects they form a longitudinal series situated in the middle of the fibre. Asso- 

 ciated with and surrounding them there is sometimes, but not always, a certain 

 amount of granular protoplasm. In the unaltered condition the nuclei are not 

 easily seen, but they are made conspicuous by the addition of acid. They may 

 contain a network of chromoplasm, in which one or two nacleoli are generally visible, 

 but frequently the chromatin of the nucleus is in the form of a spiral filament. 



Variations of structure in different muscles, correlated with differences 

 of function. In the rabbit, as especially pointed out by Ranvier and Krause, 

 certain of the voluntary muscles present differences in appearance and mode 

 of action from the rest. Thus while most of the voluntary muscles have a 

 pale aspect and contract energetically when stimulated, some such as the semi- 

 tendinosus and the soleus in the lower limb, are at once distinguished by their 

 deeper colour as well as by their slow and prolonged contraction when stimulated. 

 When subjected to microscopical examination it is found that in the red muscle the 

 fibres are more distinctly striated longitudinally and the transverse strias are much 

 more irregular than usual. The muscular fibres are generally finer (thinner) than 

 those of the ordinary muscles, and appear to have a larger amount of sarcoplasm. 

 The nuclei are more numerous and are not confined to the inner surface of 

 the sarcolemma, but occur scattered in the thickness of the fibre as well. There 

 is also a difference in the blood-supply of the two kinds of muscle, to be afterwards 

 alluded to. 



A similar difference between red and pale muscles may be also seen in the rays 

 amongst fishes. In other animals the distinction is not found as regards whole 

 muscles although it may affect individual fibres of a muscle. This is the case, 

 according to Klein, in the diaphragm, in which in many of the fibres there are 

 numerous nuclei, and these are embedded in protoplasm, which forms an almost 

 continuous layer underneath the sarcolemma. The distribution of the two kinds of 

 fibres in different muscles has been recently more especially investigated by Griitzner 



