STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. 107 



In the largest fibers in the section one can scarcely find any liposomes in the body of the fiber. 

 Arotmd the border and immediately under the sarcolemma, especially in regions which have inter- 

 cellular fat in the neighborhood, there are groups of liposomes. 



These groups are shown in the figure 10, plate vii, and are characteristic. In one fiber 144/; in 

 diameter very delicate liposomes are rather thickly dispersed in the superficial layer and more scatter- 

 ing in the central portion of the fiber. This fiber is smaller than the average of the large size and has 

 relati^-eh- more fat. 



The teased pink fibers are filled with liposomes. These are in long chains, which are quite tuiiform 

 in appearance. In the small fibers the liposomes are from i to 1.5/1 and occasionally 2 ;i in diameter. 

 In a number of instances observed adjacent liposomes have fused into oblong droplets. In certain 

 isolated fibrillae the liposomes are adherent but irregular in position. In a fiber about 150;; in diameter 

 I find that the central portion has only scattered chains of liposomes, while near tlie surface the chains 

 are more numerous. In either case the liposomes are of irregular size in the chains and not of regular 

 arrangement, as in the type from down river. The striations in this material are very narrow. I have 

 not examined carefully enough to determine the exact relation between the liposomes and the stria- 

 tions. The number of liposomes in a given area varies in different portions of the fiber. There are 

 irregular patches of fat droplets of liposomic size at the surface of the fiber. From this appearance 

 and that noted in the cross section one comes to the conclusion that these patches of liposomes are the 

 ones shown under the sarcolemma in the transverse section. The arrangement of these patches of fat 

 under the sarcolemma is partly dependent on some pressure factor. At any rate, there is a fairly definite 

 map shown by them. In some instances this may correspond with the capillar}' net. Also there are 

 numerous areas, oftentimes two or three in the same field, in which the fat is arranged in a definite 

 ring arotmd a clear area. This suggests a relation to some relatively large intercellular fat drop. There 

 is no other structure present with which such a definite arrangement of fat drops coincide, and the num- 

 ber of instances observed is too great to be a mere matter of chance. This pattern-like arrangement of 

 fat under the sarcolemma was often noticed in preparing fresh material in the field. In one of three 

 fibers of a group examined in tliis connection there were a number of fused liposomes in the chains. 

 These fusions have taken place in the chains of liposomes near the surface, but are not of the subsar- 

 colemmal group. 



Microscopic examination of Ihc caudal pink muscle (lection Mil). — The amount of intermuscular 

 fat is insignificant in this section, almost exclusively limited to the myocommata. The intramuscular 

 fat is also ver,- small. In the very smallest fibers there is still present quite an appreciable amoimt of 

 fat in small liposomes. These liposomes vary in size, about an average of 0.4/1. They are not so 

 numerous as in the same size of muscle fiber in the trunk region. There are small fibers which show 

 groups of liposomes under the sarcolemma. In the medium-sized fibers such liposomes as are present 

 are limited to the superficial layer of fibrillae and to the space under the sarcolemma. In the large 

 fibers the only trace of fat is under the sarcolemma, and that is present only in isolated regions where 

 the liposomes are of scarcely visible size. 



Microscopic examination of the trunk dark muscle {sections My, 16, 25). — Section M7 shows a com- 

 paratively slight amount of intermuscular fat. That is chiefly along the thicker connective tissue 

 strands. Among some of these strands which are more vascular the low magnification shows areas in 

 which the bordering muscle fibers are almost free of fat. The appearance suggests that the fat is in 

 process of removal. Under the 112 oil immersion it is noted tliat in the compact areas of the muscle 

 tliere are scattered droplets of intermuscular fat. The drops are comparatively small in size, 3.5 to 4 /i, 

 but occasionally as much as 12 n in diameter. 



The intracellular fat is present in medium amount. It is distributed less uniformly over the sur- 

 face of the section of the fibers. It is noticeably less in amount in the center of the section of many 

 of the larger fibers. The diminution in the amount of the fat in the middle of the fiber is primarily 

 due to a great reduction in the size rather than in the number of the liposomes. In the center of a 

 given fiber under observation the liposomes are from 0.4 to i /i in diameter, while at the sm^'ace of the 

 same fiber they are 1.6 to 2 /i in diameter. In this fiber there are fat drops under the sarcolemma which 

 measure 2.5 to 3 /i in diameter. 



The examination of a fiber bordering on one of the lightly stained areas mentioned above shows no 

 large fat droplets, and the liposomes are reduced to an average size of 0.3 /i in diameter. There is a 

 group of liposomes about 1.2 /i in diameter under the sarcolemma of this fiber at the point farthest 



