GRANULES AND FAT OF STRIATED MUSCLE 7 



Knoll ('89) concluded that the dark appearance of muscle fibers 

 is due to the presence of interstitial granules, the dark fibers, he 

 states, have many granules while light fibers are free from granules 

 or contain only a small number. Knoll ('91) described the dark 

 fibers as rich in interfibrillar substance or sarcoplasm ('proto- 

 plasmareich') and as containing many interstitial granules, while 

 the light fibers were poor in interfibrillar substance (protoplas- 

 maarm') and contained few granules. As a rule, red muscles 

 contained more dark fibers while white muscles consisted of light 

 fibers to a large extent. The dark fibers were usually of a smaller 

 diameter than light fibers. Knoll also held that in general the 

 active muscles contain a larger proportion of dark muscle fibers 

 with a corresponding increase in the number and size of the 

 interstitial granules. Schaeffer ('93) confirmed the work of Griitz- 

 ner and Knoll. He also found that dark fibers showing fixed 

 contraction nodes simulate light fibers. Bell ('11) found that, 

 in general, dark fibers contained coarse, strongly-refractive lipo- 

 somes, ' while light fibers contained small faintly-refractive lipo- 

 somes. He stained the liposomes (fat droplets) with Herxheimer's 

 solution of Scharlach R and in this way demonstrated the types 

 of fibers. 



The reader is referred to the papers of Knoll, Schaeffer, and Bell 

 for an account of the general occurrence and distribution of light 

 and dark fibers in different animals. The work of these authors 

 has shown that differences in opacity, corrresponding to light, 

 dark, and intermediate fibers, occur in the striated muscles of 

 many animals, including practically all those most commonly 

 employed in the laboratory. 



In my studies the light and dark fibers were easily observed 

 in transverse sections of fresh tissue cut on the freezing microtome. 

 The difference in opacity is most marked when the specimen is 

 mounted in normal saline and examined with low magnification, 

 the reflected light being cut off by a paper shield or by some other 

 means. The types of fibers were also demonstrated by staining 

 frozen sections with Herxheimer's Scharlach R, with Nile blue, 

 or with Cresylviolett. In the pectoral muscles of the pigeon 



