STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. 105 



for dark muscle, and it is correspondingly easy to determine whether the fat is free or under the sar- 

 colemma. The longitudinal section (L25) gives a fine confirmation of the cross section. 



The intermuscular fat is present in large quantity, the larger drops averaging from 12 to 15 fi in 

 diameter. There are many smaller droplets interspersed among the larger. 



The fat under the sarcolemma shows well both in the cross sections and in teased preparations. 

 It is seen best when the focal plane cuts the surface of the fiber. The drops are irregularly placed over 

 the surface, being held in position by the delicate sarcolemma. Wlien the focal plane cuts the center 

 of the fiber one can see that the sarcolemma incloses the fat drops. 



The intramuscular fat in the body of the fiber is uniform in its distribution, as viewed in cross 

 section. The droplets average from 2 to 2.5 fj. in diameter, many of them smaller, but some larger. 

 Rarely does one see a droplet greater than 3 /i in diameter. 



In the longitudinal sections the chains of liposomes are more numerous and longer than in any 

 tissue examined. In some fibers these chains extend across a whole microscopic field. Several fibers 

 show chains in which the individual liposomes have fused. In such case the fat is in long slender 

 rods, showing constrictions corresponding to the fibrillae (slide L46). In comparison with salmon 

 no. Ill and no. 115 from Ilwaco, this fish has as many, even more, intramuscular fat droplets, but 

 the droplets are relatively smaller. The larger droplets, which in the Ilwaco salmon measure as much 

 as 6 fi in diameter, are absent here. 



Microscopic examination of the caudal dark muscle, teased (L^S). — These teased caudal dark fibers 

 show considerable variation in the amount of loading of the fat in the different fibers present (1/12 oil 

 immersion). One fiber contains a relatively large amount of fat on the surface of the fiber, interpreted 

 as under the sarcolemma. The larger fibers show but little fat in this subsarcolemmal region. If 

 present at all, it is relatively small, running 4 to 5 fi. 



The fat within the substance of the fibers is greatly reduced in amount in comparison with the 

 fibers from the. middle of the body. The liposomic chains are not so numerous and the average size of 

 the liposomes not so great. In these caudal fibers one often finds a chain of liposomes which has become 

 fused, as in the trunk dark. In the muscle fibers least filled with fat the number of chains of liposomes 

 is very much less and the size of the liposomes does not average over 1.2 fi. 



A large salmon (no. I2§), length and weight not recorded, taken at Warrcndale, Oreg. 



Microscopic examination of the trunk pink muscle [transverse section, 1/12 oil immersion). — The amount 

 of intermuscular fat is relatively small, the drops are often large, as much as 50 ft in diameter, but they 

 are few in number — not more than i to every 3 or 4 fibers. 



The amount of fat within the fibers is obviously greater in the smaller fibers than in the larger. 

 In the small fibers, 30 fi in diameter and less, the liposomes are fairly uniformly distributed in size, 

 ranging from 0.6 to 2.5 fi in diameter, but averaging about 1 fi in diameter. The intermediate fibers 

 have the fat collected around a superficial zone about 8 to 10 /i beneath the surface of the fiber. Some 

 of the fat droplets in this region are relatively large, 4 ;« in diameter, though these are comparatively 

 rare. In the center of the fibers the liposomes are smaller, the larger ones averaging i fi. In a fiber 

 100 ft in diameter the liposomes are quite uniformly distributed over the surface of the cross section, 

 but run only 0.2 to 0.6 fi in diameter. The liposomes in the largest fibers are of practically the same 

 diameter, but not so numerous. In the largest fibers examined and in those most free of liposomes 

 there is a noticeably greater number of liposomes near the surface of the fiber. In certain of the fibers 

 these liposomes are just under the sarcolemma, between the fibrillae of the surface layer and in the 

 zone at the inner border of the superficial or palisade fibrillte. 



Microscopic examination of the caudal pink muscle. — The intermuscular fat is limited to the myo- 

 commata and to the thick connective tissue septa. 



The intramuscular fat is present as liposomes in the small and intermediate fibers and just under 

 the sarcolemma of most of the large fibers. Liposomes are distinguished with difficulty in the central 

 body of the large fibers. 



Microscopic examination of the trunk dark muscle. — The intermuscular fat is not so great in amount 

 as in no. 122, though the fat drops run up to 20 fi in diameter. There are areas over the section which 

 have practically all the intermuscular fat as well as much of the intramuscular fat removed. 



