STORAGE OF FAT IN MUSCUCAR TISSUE OF KING SALMON. II7 



Microscopic examination of the trunk dark muscle— The dark trunk fibers are very compactly arranged, 

 so that it is difficult to distinguish between the intermuscular fat and subsarcolemmal fat. But it is 

 apparent that there is a small amount of intermuscular fat. This is confirmed by the connective tissue 

 of teased muscle. The drops are of liposomic size, rarely more than 2 to 2.5 /t in diameter. 



The intramuscular fat is present in the usual localities. Under the sarcolemma tlie droplets are 

 medium in size, 1.7, 2.8, 3, and 5.4 /t in typical droplets. The sarcoplasm of tlie fibers is rather evenly 

 studded with unusually small liposomes for this type of muscle. The liposomes are even smaller than 

 in the trunk pink muscle, are condensed about the surface of the fibers and arc larger there, 0.4 to 1.2 /i. 

 In the body of the fiber tliere are fewer liposomes and the size is from 0.2 to 0.8 /(. 



The teased dark fibers confirm the above notes as to tlie fat disposal. The fibers have exception- 

 ally clear striations which average 2.6 /i in length. The fat is irregular and the liposomes of the chains 

 can not be followed in relation to tlie striations. The fat under the sarcolemma is in patches in these 

 fibers. The whole appearance of the dark fibers closely approaches that of the pink fibers of this salmon. 



Microscopic examination of the caudal dark muscle. — In the caudal dark muscle there is still enough 

 fat between tlie fibers and under the sarcolemma to give a distinct mosaic-like marking of the outlines 

 of the fibers. In some portions of the sections this surface fat is gone. 



The intramuscular fat is still much less than in the trunk dark muscle. There are fibers that 

 have the merest trace of liposomes in the muscle substance. Even in tlie fattest fibers only minute 

 liposomes are present, the smallest amounts observed in this type of muscle, except in no. 140. There 

 is the sharpest contrast between this tissue and the Ilwaco type. 



Spauning male salmon (no. 140), length gSomm., weight S, 0^0 gravis. 



This fish was selected as a type of spawning fish in good physiological condition but at the last stages 

 before death. It was taken at the United States Fisheries station at Cazadero, Greg., on the Clackamas 

 River, September 6, 1911. 



Microscopic examination of the trunk pink muscle. — There are traces only of intermuscular fat, which 

 is in fine liposome-like droplets in the larger connective tissue strands and in the myocommata. 



The small fibers still contain a sprinkling of liposomes, enough to give them a decidedly pink appear- 

 ance under the low power. The 1/12 oil immersion shows tliat these liposomes are gathered chiefly 

 around the superficial border of the fiber and that they are in groups in the neighborhood of intermuscular 

 fat. The largest liposome observed in a small fiber measured 1.4/1 in diameter, but such are few in 

 number. The average size of liposomes for these small fibers is only a fraction of a micron. 



In a large fiber under the oil immersion there are a few areas of fat in irregular-sized droplets under 

 the sarcolemma, traces in contrast with Ilwaco salmon. Through the body of the fiber there are chains 

 of finest liposomes o.i to 0.2 11 in diameter, but the chains are short and irregular. In two other typical 

 fibers in the field, one medium and the other rather small, the liposomes are present in about the same 

 number of chains as in the large fiber, but are slightly larger in size. In all these fibers the particular 

 characteristic feature is the irregularity in the chains of liposomes. The individual chains have not 

 the usual arrangement of larger liposomes in the middle of the chain and the size tapering down to small 

 ones at the end of the chain. They are irregular in size throughout the chain. 



Microscopic examination of the caudal pink muscle. — There is practically no fat in this caudal muscle. 

 The trace that is present (1/12 oil) is only enough to give a faint stain to the superficial border of occa- 

 sional fibers. There are scattered and irregular groups of a few small liposomes just at the surface of the 

 fibers. Several fibers that have been turned horizontally show no chains of liposomes. 



Teased fibers show no liposomes in the body, but occasional traces of liposomes just at the surface 

 of the fibers. These traces are definitely between the sarcolemma and the sarcoplasm, an arrangement 

 most often noted in pink fibers poor in fat. 



Microscopic examination of the trunk dark muscle. — The outlines of the trunk dark fibers are marked 

 by rather heavy rings of fat droplets. These markings are least prominent in the neighborhood of 

 vascular areas. It is not always possible to distinguish between intermuscular and subsarcolemmal fat. 

 Both are present. Most of the fat observed is judged to be under the sarcolemma. The fat drops 

 between the fibers range in size from 3 /i to 8 /i. 



The fat under the sarcolemma seems to be in rather small but numerous droplets. This fat runs 

 from 2 to 4 /I in diameter. Out in the body of the muscle fibers there is a variable arrangement of 



