STORAGE OF FAT IN MUSCULAR TISSUE OF KINtJ SALMON. 97 



Microscopic examittation of the trunk pink muscle (sections KjS, 45, K^ssS). — The intermuscular 

 fat is crowded in evcr\' angle formed by groups of fibers. The drops vary in size from small ones to 

 as high as 100 /t in diameter. The muscle fibers themselves vary greatly in size, from 50 to 300 /( in 

 diameter. In cross section the muscle fibers are oval to round in outline, the round contour of the 

 individual fibers being in sharp contrast to the polygonal shaped outlines of fibers of salmon no. 117. 



The two sections on slide K4S were made free-hand and thick in order to show the relations of 

 the intermuscular fat. The section includes a tendinous myocomma. Where the muscle fibers are 

 very close together a single row of large fat drops extends down the length of the fiber from the myo- 

 comma. In two or three regions tlie intermuscular space is filled up with two or even more rows 

 of such fat drops. These fat drops are from 50 to 60 11 in diameter. They are somewhat compressed, 

 having their long axis in the longitudinal axis of the fibers. The myocomma itself is crowded with fat. 



The intramuscular fat is present in all the fibers. It consists of extremely fine liposomes, being 

 most minute in the large muscle fibers and greatest in amount in the small fibers. They are uniformly 

 distributed throughout all of the body of the muscle fiber, with the exception of the narrow ring of 

 band-shaped fibrils which forms the sin^'ace layer. 



The chains of liposomes are rather evenly distributed throughout the substance of the large fibers, 

 but consist of very small liposomes from those just identifiable up to 0.3 /i. In the medium-sized fibers 

 the liposomes are somewhat larger and in the smaller fibers considerably larger than in the ones just 

 described. In the latter the liposomes reach the diameter of 1.5 fi, though the average is less than iji. 

 In one fiber 56 /t in diameter the liposomes were in unusually long chains and large in size, similar to the 

 arrangement in dark muscle at a late stage in the resorption. Several liposomes in this muscle were 

 measured which were 2 /i in diameter, but the average was from i to 1.2 /(. Figure 8, plate vi, shows the 

 distribution of fat in the trunk pink of salmon no. 118. 



Pink muscle from the belly shows an even greater amount of intermuscular fat; also minute 

 liposomes in chains throughout the substance of the fibers. 



Microscopic examination of the trunk dark muscle (K41 and 42, transverse sections). — There is a large 

 amount of intramuscular fat in the lateral dark muscle of fish no. 118. The size of the fat droplets in 

 this region is from g to 12 /i in diameter. In a certain interseptal region the fat drops are large, running 

 as much as 60 /i in diameter. This fat belongs to the adipose tissue proper. A noticeable difference in 

 the staining character is present between it and the fat in general; i. e., the large fats are less red. The 

 muscle fibers of this section are so compact that it is often difficult to determine whether a given fat drop 

 is within the sarcolerama or without. It is judged that a rather large proportion of the fat which is massed 

 around the surface of the fiber is under the sarcolemma. The section throughout its whole extent shows 

 an enormous quantity of fat massed along the lines which separate the fibers. 



The teased dark muscle (slide K52) shows numbers of relatively large fat droplets along the sides 

 of the fiber wall and adherent to the protoplasm. These droplets are smaller on the average than those 

 of the cross section which were judged to be intermuscular. 



Within the dark muscle fibers of this teased material the fat is present in masses — no other word 

 seems adequately to express the condition. There are numerous fibers, in fact nearly all of them, in 

 which many chains of liposomes are displaced by long masses or rods of fat. Undoubtedly, these rods 

 of fat have been produced by the fusion of liposomes in the loading of the fiber with a higher percentage 

 of fat than is found when liposomes are typically present, as, for example, in salmon no. 132. In the 

 present section there are four such rods in one microscopic field. In another similar field there are six. 

 In a fiber 40 /i in diameter these rods continue unbroken for as much as 126 ft. They are located in the 

 areas between the bundles of fibrillar, where one finds in the ordinar>' loading either chains of liposomes 

 or, at most, short oblong droplets. 



There are fibers in this teased material that have a somewhat less quantity of fat than that described 

 in the last paragraph. In one such typical case the smallest liposomes observed measure 1.5 to 2.5 ;i. 

 In close proximity to this last chain of liposomes there is a chain of fused liposomes, i. e., a rod, which is 

 continuous for 120 ,u. This rod has, however, several partial constrictions which undoubtedly represent 

 points where in the earlier stage of fat deposit the rod is discontinuous. 



In the transverse section (1/12 oil immersion) the fat is crowded into the fiber in a way comparable 

 only to no. in. The whole surface of the field is taken up with fat droplets almost as thick as they can 

 stand. There are relatively few liposomes that measure less than 1.8 /i in diameter and the size varies 

 up to 5 /i. There are chains of these smaller liposomes throughout the protoplasm, even in fibers obviously 

 distorted by the long rods of fat. 



