STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. 93 



degeneration. These changes are almost wholly in the direction of retrogression of 

 structure. 



In the muscular tissue there are two factors mentioned above which are interpreted 

 as changes that have come on in the amount and distribution of fat in the muscle since 

 the beginning of the migration fast. These are, first, the abundance of intracellular 

 fat laid down in the pink-muscle fibers; second, the evidence in the dark-muscle fibers 

 of removal of fat. Interpreting these two phenomena broadly one may assume that 

 there has occurred already in the best conditioned channel fish a using up of a certain 

 amount of fat. Considered from the standpoint of percentages this amount has not 

 reduced the total storage enough to be readily measured by the microscope except in 

 the second case. In the poorer fish it is quite obvious that fat is disappearing, undoubt- 

 edly due to the prolonged fast. This is especially shown in the Bakers Bay type illus- 

 trated by no. 117. This interpretation is supported by the quantitative chemical 

 determinations of fat. 



There is absolutely no microscopic evidence which can be legitimately interpreted 

 as meaning a fatty production from the disintegration of protoplasm. If, therefore, 

 one could follow back the physiological condition of an Ilwaco salmon to that point 

 in its history where it first ceased to feed, and would examine its tissues for the loading 

 of fat, he would find that this time represented the maximum amount of fat present in 

 the animal. In other words, this stage of the beginning of the fast, i. e., end of the 

 feeding period, represents the climax of fat storage during the salmon's history. The 

 microscopic picture obtained b}' a study of the Ilwaco specimens is therefore applicable 

 to this normal stage, provided, first, that the intramuscular fat of the pink muscle be 

 omitted, and, second, that all the areas of dark muscle which appear to be losing fat 

 be considered as uniformly filled with fat. Figure 8, plate vi, representing the fat in a 

 cross section of pink muscle of salmon no. i iS from Ilwaco, would, if the intramuscular 

 fat were eliminated and the intermuscular fat increased in quantity, represent very well 

 my conception of the quantity of fat in this tissue when the fast begins. So also in 

 the dark muscle, figure 3, plate i, would serve as a type for the dark muscle at the 

 beginning of the fast. These figures fail in the fact that they have too little inter- 

 muscular fat to represent the normal, but the percentage difference is one which can not 

 easily be estimated by the microscope. Salmon no. 114 has nearly twice the amount 

 of fat in the pink muscle shown by no. 118. This fat is wholh' intermuscular and would 

 show in the microscope in the form of larger drops rather than in a greater number. 

 Judging wholly by the microscopic comparisons, one would never judge that the difference 

 is as great as that revealed by the chemical determinations of the fat percentages. 



PROTOCOLS. 



Male salmon (no. Ill) length g^o mm., weight 13,7^6 grams, taken between the jetty and the black buoy at 

 the mouth of the Columbia River, August J, IQII. 



This was a clean, bright, silver)' salmon of the short, deep tj-pe. It is a perfect looking specimen 

 of the sea type. It was caught with a gill net by Mr. Cliff Sweeney. This salmon had all the appearance 

 of a first-class, verj' fat specimen. Its flesh looked oily and there was a thick layer of cutaneous fat. 



Microscopic examination of trunk pink muscle, teased [slide f6). — These isolated fibers of pink muscle 

 are simply crowded with liposomic fat. The fat is arranged in longitudinal rows or chains of liposomes 

 between the fibrillse which bear relation to the striations. The liposomes are from 0.2 /t or less to 2 11 



19371°— vol 33—15 7 



