Il6 BULLETIN OF THE BUREAU OF FISHERIES. 



fibers. In other regions one can as definitely say that there is fat beneath the sarcolemma but outside 

 the substance of the fiber. At the border of the section a number of fibers have been slightly split 

 apart and some turned in a horizontal position. These fibers confirm the above. 



As a rule, through the section there is only a small amount of intramuscular fat in chains of liposomes 

 through the bodies of the fibers. In the horizontal fibers the size of the liposomes is shown to be from 

 0.4 to 1.5 /( in diameter. The majority of the liposomes are of the larger sizes. 



The striking characteristic of this tissue is the great differentiation as between the amotmt of fat 

 in the body of the fiber and at the surface. There is apparently more fat in the dark muscle of this 

 fish than in fish no. 128 and no. 129 from Celilo, imdoubtedly more than in fish no. 131 of Cazadero, 

 but the bodies of the fibers contain relatively less. 



Microscopic examination of the caudal dark muscle. — The amoimt of intermuscular fat is greatly 

 reduced over that of the trunk muscle, the droplets are smaller, and they are not so numerous as in that 

 region. They are, however, sufficient to give a mosaic-like appearance to the section. 



The intramuscular fat is extremely small except such as lies just imder the sarcolemma. Certain 

 of the sections show the ends of the fibrillae clear and sharp. The pattern is the same as shown in figure 

 7, plate V, except that there are no fat spaces present. This certainly indicates that the muscle has 

 not degenerated, yet nearly all the fat characteristic of the normal muscle is absent and there are only 

 a very few liposomes in the fibers near the surface. 



Spawning male salmon {no. ijS), length S40 mm., weight y,^J0 grams, from the spawning pens of the 

 United States Fisheries Station, Cazadero, Oreg., on the Clackamas River, September 4, igii. 



This male salmon was one-half to three-fifths spawned. Color brassy, with black spots. Soft dorsal 

 decayed and one fungus spot on dorsal fin. A fish in good condition but in late stage of exhaustion. 

 It would probably have died in the course of 24 to 36 hours. 



Microscopic examination of the trunk pink muscle. — The pink fibers of salmon no. 138 are not plump 

 and round as in fish no. 118. On the other hand, their outlines form irregular polygons. Even the 

 smaller fibers have this shape. The larger fibers bear histological evidence of great decrease in size 

 (samples one day in formalin). A set of cross-sectional measurements show the following: 40 by 80, 

 60 by 70, 80 by 140, and 100 by 220 /i, outlines all very irregular. The cross sections show both the 

 striations and the fibrillae very nicely. 



The sections are free of intermuscular fat except for a few of the finest droplets and liposomes. 

 In a large section there is one such group of fat droplets in a large mass of connective tissue. There 

 are a few thin strands of connective tissue between the fibers, and these carry occasional fat droplets 

 not over 3 to 4 /i in diameter. The larger size is rare, though fat drops in the same locality in no. 118 

 from Ilwaco measure 100 /i and more. There are a good many tiny liposomes in this connective tissue, 

 though the mass is extremely small. 



In contrast to the dearth of fat between the fibers there is an imexpectedly large quantity of intra- 

 muscular fat within. As usual this fat is in liposomes. The size and number are both greater in the 

 smallest fibers, yet the largest fibers have a pretty even sprinkling of liposomes of extremely minute 

 size. I can not find a single fiber but that has some fat within its protoplasm. In the smaller fibers 

 there is a great amoimt of fat around the siuface in the region just under the sarcolemma. Taking the 

 small fibers as a whole, it seems that the liposomic fat is present in a greater number of droplets and 

 in slightly larger droplets than in the poorer specimens from Warrendale. There is decidedly more 

 intramuscular fat than in fish no. 126 from Warrendale. 



The teased fibers give a beautiful confirmation of the notes made on the cross sections. They show 

 one variation from the typical arrangement of liposomes, namely, that the deep-lying liposomes are not 

 in such regular rows as in the normal. The liposomes have a very irregular appearance, as if the smaller 

 liposomes had disappeared. Those liposomes that are left are unusually large and uniform in size for 

 pink fibers. The rows that are most definite and uninterrupted are located near the surface of the fiber. 

 The larger liposomes are from 2 to 2.5 ,u in diameter. 



Microscopic examination of the caudal pink muscle. — The caudal pink muscle sections are free of all 

 but traces of fat. The intermuscular fat is limited to a few droplets in the myocommata. Only a few 

 irregular chains of very small liposomes are present in the fibers. These are more distinct in the smaller 

 fibers. The striations are distinct and clear, but the fat is faint and scarcely distinguishable. 



