Structure of Suiootli Muscle. 525 



While the internudal segments of the libers are lightly staining and 

 distinctly fibrillated, as in I'igs. 2, 5, 11, 20-22, 35, 36, the contrac- 

 tion nodes in ordinary material appear homogeneous and are deeply 

 staining. This condition has been described by numerous investi- 

 gators and by them has been variously interpreted. Kolliker, 1849; 

 Roule, 1890, ISUl; Schaffer, 18DU ; Heiderich, 1902, and Soli, 

 lUOG, 1907, considered the homogeneous nodes the contracted por- 

 tions of the fiber. Ilenneberg, 1901, because he found that these 

 nodes in his fixed and stained preparations were usually of smaller 

 caliber than the internodal seginents, descril)ed them as uncontracted, 

 the internodal segments as the contracted portions of the fiber. His 

 work was done upon the carotid of the ox. Heiderich demon- 

 strated quite conclusively on the same material that the homogeneous 

 nodes are nodes of contraction. That Henneberg found them smaller 

 in cross section of fixed material than the internodal segments Hei- 

 derich explained as due to their being more subject to shrinkage in 

 some reagents than are the fibrillated internodal segments. He 

 tested a large number of fixatives. With some the internodal seg- 

 ments were larger than the homogeneous areas, with others smaller. 

 In fresh material the homogeneous areas were always of greater 

 caliber. The fact that the nuclei shorten and thicken at the homo- 

 geneous areas while the elastic fibers run more wavy and the colla- 

 genous fibers are more condensed at these points he took as additional 

 evidence that the deeply staining homogeneous nodes are the contrac- 

 tion nodes. Soli, 1906, 1907, in the stomach muscle of birds found in 

 fixed material that the deeply staining homogeneous areas are invari- 

 ably of greater caliber than are the fibrillated portions of the fiber, 

 so he considers the former the contraction nodes. 



In most of the material investigated by the author the contraction 

 nodes resemble those described by Soli, 1906. That is, they occur 

 as deeply staining thickened nodes of the fiber, Figs. 2, 11, 12, 20-22, 

 30, 37. With ordinary stains, such as luTcmatoxylin eosin or in iron- 

 hsematoxylin, after the usual difFercutiations thoy appear homogene- 

 ous. Muscle of this tyi^e was found throughout the digestive tract 

 of chicken and mammals and in the urino-genital tracts of mammals. 

 The most pronounced thickening of the fiber at the contraction node 



