GRANULES AND FAT OF STRIATED MUSCLE 43 



arrangement of the granules and fat droplets within muscle fibers 

 is not dependent upon any connection with a fibrous net-work 

 but is determined solely by the position of the membrane of Krause, 

 the size of the granules, and the pressure of the muscle columns. 



The true interstitial granules are of a soft, plastic substance 

 and have no limiting membrane. 



The exact chemical nature of the true interstitial granule is 

 unknown. They are certainly not composed wholly of fat, though 

 they contain an alcohol-soluble element. As was suggested by 

 Regaud, they may be an albumino-lipoid. 



Many fat droplets in muscle fibers are not preserved by for- 

 malin fixation. After a variable length of time in formalin fixa- 

 tives the droplets may disappear. Fresh tissues must be used if 

 all the droplets are to be demonstrated. This confirms a conclu- 

 sion drawn by Bell. 



Fat droplets in muscle fibers are frequently stained but faintly 

 or left colorless by the commonly used solutions of Scharlach R 

 and Sudan iii in 70 per cent alcohol. Alkaline-alcoholic solu- 

 tions of Scharlach R applied to fresh tissue stain all the fat drop- 

 lets of muscle fibers. By this method preparations may sometimes 

 be shown to be loaded with fat droplets when none are stained by 

 the simple alcoholic solutions. 



Nile blue sulphate and Nile blue chlorhydrate color all the fat 

 droplets of muscle fibers when fresh tissue is used and stained 

 sections are placed in alkaline water or mounted in an alkaline 

 medium. The droplets are usually colored red, but under certain 

 conditions they stain blue. With favorable material, pectoral 

 muscles of pigeon and bat, after a short formalin fixation, both 

 true interstitial granules and fat droplets may be stained in the 

 same preparation, the former blue, the latter red. 



Many fat droplets of muscle fibers are not blackened by osmium 

 tetroxide. 



For the most part the fat droplets of muscle fibers are neutral 

 fat, glycerin esters of fatty acids. No convincing evidence has 

 yet been presented to show that the fat droplets contain any 

 substance other than neutral fat. They may not be pure neutral 

 fat but it is improbable that they contain any considerable amount 

 of albumin or other non-fatty substance. 



