120 STUDIES IN ADVANCED PHYSIOLOGY. 



themselves are made up of component pieces, in some way 

 attached end to end to make up the entire length. These 

 component parts of each fibril are called the muscular units 

 or the sarcomeres. When the muscle fibres break up into 

 these disks the line of cleavage runs through the middle of 

 the light band. With very high powers there may be dis- 

 cerned at this point a little darker line, which is probably a 

 membrane, and has been called Krause's membrane. In 

 the longitudinal splitting of the fibre into the fibrillse, such 

 as a specimen of muscle hardened in alcohol readily does, 

 the lines of splitting seem to be in a peculiar inter-columnar 

 substance which binds the individual fibrils together. 



From these two manners of breaking up it can easily be 

 seen that the individual sarcomere is that portion of a fibril 

 which extends from the middle of one light band, or from 

 Krause's membrane, to the middle of the next white band. 

 It is, therefore, light at both ends and contains its dark 

 band in its middle. These sarcomeres, lying in even rows, 

 give to the entire muscle fibre the banded appearance. The 

 light material next to Krause's membrane seems to be 

 a thin, active kind of protoplasm called hyaloplasm. The 

 dark band in the middle really consists of two dark bands 

 separated through the middle by a light band called the 

 band of Hensen. These dark bands, as may easily be seen 

 by referring to the diagram, have little comb-like projec- 

 tions extending up and down, which next to the band of 

 Hensen are united together on each side to a common base. 

 Whether these prongs or teeth are solid, or whether they 

 are hollow tubes, cannot be determined. They probably 

 consist of a firmer kind of protoplasm, and are in each sar- 

 comere called the sarcosome. The transparent columnar 

 substance, which seems to cement the individual fibrillae 

 together, is of a similar kind of protoplasm called sarco- 

 plasm. Thus the individual sarcomere would have hyalo- 

 plasm at its ends, have the sarcosome or dark portion in 

 the center, and be connected with neighboring sarcomeres 

 by the intermediate sarcoplasm. 



