GRANULES AND FAT OF STRIATED MUSCLE 11 



in certain individuals, show only light fibers. It is clear that 

 dark fibers do not necessarily give a red color to muscle nor does 

 the presence of light fibers in red muscle make it less red in appear- 

 ance. 



According to Krause. ('11) red and white muscles in the rabbit 

 differ only in number and arrangement of blood vessels and in 

 amount of connective tissue. I am unable to say to what extent 

 the red color of muscle is due to the presence of blood. Lelievre 

 and Retterer ('09) studied the structural differences between the 

 red and white muscles of the rabbit. They concluded, among 

 other things, that the membrane of Krause (Z, Strie d'Amici) 

 is absent from white muscle (adductor magnus) . I have examined 

 the fibers of the adductor magnus of the rabbit and find the mem- 

 brane of Krause present and clearly visible in both fresh and 

 fixed preparations. 



c. Morphology and position of fat droplets 



Krause (73) observed a regular arrangement of the interstitial 

 granules in transverse rows situated in segment / on either side 

 of Krause's membrane, Z. The observations of Krause have 

 been confirmed by Retzius ('90), Arnold ('00), Holmgren ('07,- 

 '10), and many others, and it has also been observed that the posi- 

 tion of the granules as described by Krause applies to that of 

 both the true interstitial granules and fat droplets. Retzius, 

 Holmgren and others have described large interstitial granules 

 as occurring in the anisotropic segment Q, (Briicke's disc). 



The fat droplets of muscle fibers are in general spherical. Their 

 form may be modified by the pressure of the muscle columns. 

 Droplets that have a diameter exceeding one micron frequently 

 show a certain amount of elongation in the direction of the longi- 

 tudinal axis of the fiber. Exceptionally, the longitudinal diame- 

 ter of elongated droplets is nearly twice the transverse diameter. 

 Upon contraction of the fiber, droplets become more spherical or 

 even flattened in the transverse direction. Occasionally, and 

 especially in human muscle, the fat has a granular form, the evenly 

 rounded contour of droplets being absent. Possibly this is due 

 to post mortem changes. I am not here referring to the pigment 



