STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. lOI 



the portion of the tiber opposite the blood vessel will have a relatively high content of fat; 

 fourth, as a rule the intermuscular fat in contact with the opposite outer border of the 

 fiber will still be present. 



The teased fibers of this dark muscle show instructive variations. Different lengths 

 of one and the same fiber show wide variation in the loading of fat. This is expressed 

 especially through the variation in size of the liposomes. But if the fat is very light 

 in amount there will also be a variation in the number of liposomes. Careful focusing 

 will always bring out the fact that the richer portions of the fiber will have a relatively 

 large amount of fat under the sarcolemma. In many instances the liposomes in the 

 chains will have fused, forming slender fat rods showing constrictions at the point of 

 fusion. The poorer areas in the fiber will show a small amount of fat under the sarco- 

 lemma, smaller liposomes in the chains and little or no fusion. Where the fat is almost 

 completely eroded the number of liposomes will be obviously reduced. In this case the 

 reduction takes place more completely near the center of the fiber as compared with its 

 superficial area. 



In numerous instances at the other stations, as well as at Warrendale, I have 

 noticed that while the fat is being eroded there will appear variations in number and 

 arrangement of fat droplets under the sarcolemma. In a teased fiber a rather definite 

 pattern will often be noted in this subsarcolemmal fat, a pattern which coincides with 

 the blood vessels, the pattern being marked by rows of very small droplets along what 

 would correspond to the border of the capillaries. Also small rings of droplets will 

 appear at various points, sometimes in groups. These rings of droplets are arranged 

 around a clear center. They are interpreted as part of the process of erosion of large 

 intermuscular fat drops. As lipolysis goes on, the fat that is dissolved away from the 

 large fat drop will often be redisposed in small droplets within the sarcolemma around 

 the area which is being compressed by the large drop. 



Caudal dark muscle. — The caudal dark muscle of the Warrendale fish varies through 

 even a wider range of fat content than the corresponding muscle from the trunk region. 

 There is alwajs considerable fat in the myocommata, but the amount of intermus- 

 cular and intramuscular fat varies exceedingly. 



In the fatter fish the intermuscular fat is reduced in the number of droplets present, 

 but particularly in their size. In no. 125 there is practically no fat in the caudal dark 

 muscle. 



In this salmon certain of the dark fibers are absolutely clear of fat within the 

 fibers, and the fattest fibers observed contained only a sprinkling of liposomes around 

 the superficial areas with a trace in the center of the fiber. The whole muscle is as 

 nearly fat free as any dark muscle examined. It is noticed here also, as in the trunk 

 muscle, that the fibers freest of fat lie in the neighborhood of small blood vessels. 



In a few scattered fibers in the caudal dark muscle of no. 125 an appearance is 

 noted for the first time that is suggestive of a disintegrative process. We have not been 

 able to convince ounselves that these fibers are actively breaking down, but they cer- 

 tainly do show appearances suggestive of the initial stages of water absorption charac- 

 teristic, for example, of cloudy swelling. The fibers stain lightly in a way which 

 characterizes an early stage of muscle degeneration. These fibers also contain small 

 transparent, highly refractive and lightly stained granules. The stain does not have 

 the usual appearance of fat stain — that is, the color is not the brick red of the scarlet 



