STORAGE OF FAT IN MUSCUI^AR TISSUE OF KING SALMON. II 3 



a few small liposomes in irregular groups. At best this quantity and distribution can 

 be called only a trace. 



Trunk dark muscle. — In the dark muscle there is no intermuscular fat, or if any is 

 present at all it is in tiny droplets in those localities which contain the greatest amount of 

 connective tissue. In a cross section and in a low-power field one might see two or 

 three such areas. 



The intramuscular fat in the dark muscle has markedly changed in its appearance 

 and arrangement. The relatively large droplets characteristic of the normal tissue, 

 often measuring as much as 6 ft in diameter, have practically disappeared in this stage. 

 In place of the large droplets the dark muscle now contains a much greater number of 

 relatively very small sized droplets of the type described as liposomes. Also the fat 

 droplets under the sarcolemma are now reduced to liposomic size, not larger than 2 /« in 

 diameter and averaging about i /(. In a cross section these tiny fat drops around the sur- 

 face of the fiber and within the sarcolemma form definite rings which mark the outlines 

 of the fibers. Examination under the 1/12 oil immersion shows that many of the drop- 

 lets entering into the composition of this superficial layer of fat are wedged in between 

 fibrillae. Within the central substance of the muscle the liposomes are now interfibrillar 

 in arrangement. They are small in size but numerous and comparatively evenly dis- 

 tributed through the sarcoplasm. This description applies to the trunk dark muscle 

 of the fatter spawning salmon. The poor salmon do not have so many liposomes in the 

 deep sarcoplasm and diff'erent individual fibers vary greatly in their fat content. 



In the teased dark muscle fibers from the trunk it is noted that the most fat lies 

 just under the sarcolemma, but that it is very irregularly placed. The droplets are small 

 and seldom exceed 2 fi in diameter. There are a few chains of liposomes in the body of 

 the fiber, but these chains are widely separated and consist of extremely small liposomes. 

 The largest liposomes are about 0.4 fi in diameter in fish no. 139. In no. 140 the sur- 

 face of the fibers has irregular fat droplets often running as much as 3 /z in diameter. 

 But distributed through the substance of the fiber there are only traces of fat except at 

 the very superficial sheet of sarcoplasm where the liposomes are measurable. 



Caudal dark muscle. — In the caudal dark muscle there is still some considerable 

 quantity of intercellular fat, especially in salmon no. 138, although this fat is less than in 

 the lateral dark muscle of the same specimen. 



Within the sarcoplasm of the fibers there are numerous areas in which there are 

 only traces of fat. Even at the surface of the fiber there is often only a trace of fat. 

 Under the .sarcolemma the fat is in isolated groups of liposomes measuring only a 

 fraction of a micron. 



In fish no. 139 there is more fat in the caudal dark muscle, especially under the 

 sarcolemma, where the droplets measure from i to 3 /i. Different portions of the sec- 

 tion show great variation in the amount of intracellular fat. These areas are similar to 

 that noted in Warrendale fishes no. 125 and no. 126. In fibers bordering on these 

 vascular areas the fat droplets are removed from under the sarcolemma, and are absent 

 except for traces in the body of the fiber. 



In comparing the amount and distribution of fat in the Cazadero specimens it is 

 obvious that the total percentage amount of fat is profoundly reduced. On the other 

 hand, it is apparent that this reduction has taken place chiefly in the intercellular fat. 

 The extreme case of exhaustion shows practically no fat either between or within the 



