STORAGE OF FAT IN MUSCULAR TISSUE OP KIMG SALMON. IO3 



The largest intramuscular liposomes average 3 n in diameter, but there are many smaller liposomes. 

 There are rings of small droplets aroimd the border of the muscle, these averaging 4 /< in diameter. This 

 superficial fat sharply marks the boimdaries of transparent cross sections forming a definite mosaic imder 

 the low magnification. It is almost wholly intramuscular fat lying under the sarcolemma. 



Male salmon (no. 121), length g^o mm., weight not given. 



A first-class fish from the McGowan seining grounds, i},4 miles below Warrendale on the Columbia 

 River. The testes two-fiftlis developed. 



Microscopic examination of the trunk pink muscle {transverse section, Li). — The amount of intermuscular 

 fat is intermediate between salmon no. 115 and no. 117 from Ilwaco. The fat droplets between the 

 muscles are many of them relatively large but not so numerous, and do not average so large as in no. 118. 

 The largest drops are from 45 to 55 fi in diameter. The fibers themselves are somewhat more compact 

 in arrangement, but the outlines of the fibers in cross section are less smooth and circular than in no. 115, 

 but not so angular, and the fibers do not seem so much compressed as in fish no. 117. 



The surprising fact is the great amount of intramuscular fat. This fat is most thickly deposited 

 through the small fibers, where the liposomes have a size from i to 2 /t in diameter. These liposomes 

 are quite imiformly distributed through the substance of the small fibers. An occasional fiber will 

 have its liposomes more thickly set around the superficial border. In certain of the smallest fibers, 

 an example 75 ;i in diameter, also in other regions of the section, there is fat in relatively small droplets 

 just outside the surface of the sarcoplasm and under the sarcolemma. 



Liposomes are present in the largest fibers also, but are exceedingly small and not so plentiful in 

 the body of the fiber. In these very large fibers many liposomes are found between the fibrillse near 

 the surface of the fiber. They appear as if the liposomes were formed just imder the sarcolemma and 

 between the fibrillae of the most superficial or band-shaped layers. In the inner borders of the band- 

 shaped fibrils there is a second zone where tlie liposomes are present in relatively greater numbers. 

 The liposomes are not larger but more numerous in this zone. 



Microscopic examination of the caudal pink muscle {Lq, 10, and II). — Sections were preserved for 18 

 hours in formalin. The fibrillae show well indeed. The surface layer of band-shaped fibrillae are in 

 contrast to the smaller fibrillse of the body of the muscle. The fibers are compact in arrangement, but 

 retain a certain amount of round contour which characterizes muscular tissue in prime condition. The 

 following points characterize the tissue: (a) There is very little, almost no intermuscular fat in the 

 section. Here and there a small droplet is found in the angles between the fibers. The largest one 

 observed is only 18 /; in diameter, (i) The outlines of the fibers of the caudal pink muscle are defi- 

 nitely marked by very small fat droplets, measuring from i to 2.5 /i in diameter, many of them even 

 smaller. The point is difficult to determine, but the droplets seem to be within the sarcolemma. 

 (c) The caudal pink muscle fibers are relatively low in liposomes. The smallest fibers contain only a 

 few liposomes. The fibers measuring from 50 to 100 /i in diameter have easily identified liposomes, 

 but the larger fibers are free of liposomes in all but the extreme superficial part of the fiber (1/13 oil 

 immersion.) The liposomes in the smaller fibers are chiefly around the outer third of the muscle. 

 In the central portion of the fiber there is not more than one-fourth as much stainable fat as in this 

 superficial rim. 



Microscopic examination of the trunk dark muscle {transverse section, L^ and 6). — ^The lateral dark 

 muscle shows an amount of fat greater than in no. 117, but not so great as in no. iii. The fibers are 

 compactly arranged everywhere in the dark, and imder the low magnification their outlines are marked 

 by the excess of fat in that zone, the fat droplets averaging from 4 to 6 /i. 



In some of the angles between fibers and in certain regions where the connective tissue is greater there 

 is unquestioned intermuscular fat. The size of these drops runs from 10 to 15 u in diameter. Along 

 one exceptionally thick septum this intermuscular fat is absent. The section has the appearance which 

 indicates the process of resorption of fat (under the 1/12 oil immersion). 



The sarcoplasm of these fibers is full of small fat droplets almost as large as those in no. 115. The 

 droplets are too large to be called liposomes, though every gradation exists between liposomes i /( in 

 diameter up to these larger droplets which average 3.6 to 4 /( in diameter. There are certain fields of 

 the section which contain relatively less fat in the sarcoplasm, the fat droplets being almost gone and 

 the liposomes relatively smaller but thickly distributed. In these fields there is also relatively less fat 

 around the border of the fiber, i. e., less fat under the sarcolemma. 



