STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. 95 



more numerous. The liposomes appear as rows running between the fibrillse which the oil immersion 

 lens shows have an arrangement with reference to the cross striations. In one fiber six striation 

 segments have a length of 8 /i, an average of 1.3 ,« per striation. The liposomes that are spaced with 

 reference to these particular striations are from 0.4 to 0.6 /< in diameter. The arrangement of fat in 

 this group of fibers is very like the arrangement in the dark muscle of the lateralis superficialis. 



Masseter or cheek muscle {transverse section, Jg). — The fibers of the cheek muscle vary considerably 

 in diameter, running from 30 up to no a. This transverse section has a medium amount of intermus- 

 cular fat distributed in large droplets from 60 to 70 /( in diameter. There are also numerous fat drops 

 from 15 to 20 ;( in diameter. 



The muscle fibers themselves are much split up by ice crystals in sectioning, yet it is clear that the 

 fibers contain intracellular fat. This fat is greatest in amount in the smallest fibers, where the droplets 

 are about o. 5 /( in diameter. The larger fibers also contain intramuscular fat, but the droplets are smaller. 



Male salmon {no. I15), length Q40 mm., weight 12,225 grams, caught in the Columbia River channe:l just 



above Sand Island, August ", igil. 



This salmon was a clean fish, free of sea lice; testes slightly developed and dark venous red in 

 appearance; stomach relaxed, 5 cm. in diameter with mucous content. Dark muscle teased imme- 

 diately in physiological saline and figured. 



Microscopic examination of trunk pink muscle leased in physiological saline. — These muscle fibers show 

 extremely fine liposomes within the fiber. In larger fibers the liposomes are difficult to distinguish, 

 but are readily seen in the small ones. The amount of intramuscular fat is not so great as in the trunk 

 pink muscle of no. 113. Section Jgq, stained with haematoxylin only, differentiates the interfibrillar 

 sarcoplasm in such a way as greatly to emphasize the outlines of transparent liposomes. The liposomes 

 themselves appear highly refractive and have not taken more than a trace of the stain (i/i2oil immersion). 



Microscopic examination of trunk dark muscle teased in physiological saline {J46). — A drawing of a 

 fiber from this slide is presented (fig. i) showing the fat throughout the dark muscle. Practically all the 

 fibers in this slide are loaded dowTi with fat. There is an enormous quantity of fat present, more than one 

 can adequately represent by any graphic method. The fat drops within the fiber are relatively large 

 and are so numerous that they push out the sarcolemma, making its outlines irregular. The drops are 

 somewhat oval in shape, measuring 8 by 13, 5 by 6, 7 by 16 /(, and smaller. The diameters of some of 

 the fibers are 35, 36, 40, and 45 /i. The fat droplets are in rows. They are relatively large in almost 

 all parts of the field. This is due to the fact that the liposomes have grown in size until adjacent ones 

 have fused, a condition throughout the fiber. 



With the fusion of droplets tlie resultant is an oval mass with the long axis with the interfibrillar 

 space. As the fat mass has grown the fibrils have been forced out of their normal relations. Where the 

 drops lie outside the sarcoplasm and under the sarcolemma this membrane is seen to be pushed ovit in 

 numerous irregular protuberances. This section is unusually clear and transparent, probably because 

 it was not subjected to formalin. 



Female salmon {no. 116), length <?~5 ynm., weight 14.530 grams, caught in the channel of the Columbia River 

 opposite the lower end of Sand Island, .August S, igil. 



A Vjright silvery fish, no sea lice, stomach small and contracted with thick walls; intestine one-half 

 as large as in no. 115; ovaries relatively large, weighing 965 grams. 



Microscopic examination of the trunk dark m.uscle {slides f 77-91). — The trunk dark muscle of this fish 

 has less fat than either no. in or no. 115. The larger fat drops are between the fibers. They measure 

 12 to 14 /I, but the average is not much over 7 /(. 



The intracellular fat is in smaller droplets, from a fraction of a micron to 3 and 4 /i in diameter. 

 There is a massing of the fat droplets around the surface of the fibers. 



A series of teased preparations were treated in various ways to test the method The fresh muscle 

 teased in physiological saline is more transparent than the other preparations and the fat gives the 

 appearance of a greater quantity, largely because it is more clearly distinguished. Fibers teased in 

 formalin were very opaque. Those teased in alcohol were somewhat intermediate in character between 

 the saline and the formalin preparations. 



