STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. 1 35 



Also the group of dark muscle fibers represented in the musculus superficialis lateralis 

 has already been mentioned as lipase producing tissue. But when all the less important 

 sources which have been discussed are left out of account there still remains an adequate 

 lipase producing mechanism in the pancreas and in the granule cell layer of the alimentary 

 tract to account for the presence of sufficient lipase in the blood and tissues to meet 

 the need of the fat transference that we have under discussion. Histological evidence 

 has been given to show that there is no diminution of the activity of the pancreas at 

 the inauguration of the fasting period. If the pancreatic lipase production even remain 

 constant then the amount of lipase which this gland will produce as an internal secretion 

 will tend to raise the total lipase of the blood and tissues. The lipase that is consumed 

 in the process of digestion during the feeding period will now be left to be thrown into 

 the circulation. It follows that there will be an increase in the percentage of lipase in 

 the blood, therefore, according to Loevenhart, an increased solution of the fats with 

 which this lipase comes in contact. These fats are the stored fats. An increased solu- 

 tion of the stored fats will raise the fatty acid and glycerin content of the tissue fluid 

 and the blood. The inevitable result will be an increased supply of these fat cleavage 

 products to the active muscular tissues. This supply will diffuse through the muscle 

 spaces, the sarcolemma, and throughout the sarcoplasm of the muscle fiber in an ever 

 increasing quantity. Since the relative amount of activity of the muscles can not be 

 assumed to change, i. e., is comparatively constant, it follows that the percentage 

 amount of fat will increase within the active muscle fibers. 



It is shown on page 81 that the pink muscle fibers contain no intramuscular fat 

 during the feeding stage, or at most, only a trace of such fat at maturity. This is only 

 another way of saying that the consumption of fatty substances in the muscle fibers of 

 the feeding salmon is in balance with the fatty bodies penetrating the fibers. There is 

 never a sufficient excess of fatty acid and glycerin within the fibers to produce resynthe- 

 sis and deposition of the fat in \4sible form. But with the increasing percentage of 

 these substances penetrating the fiber after the fast begins there will be a synthesis of 

 neutral fats and these will be deposited and can be identified. The liposomes present 

 in the lateral pink muscle of the salmon taken at Ilwaco represent such deposits that 

 have taken place since the beginning of the migration. The amount of neutral fat 

 present in the pink muscle fibers is a measure of the excess of fatty acids and glycerin 

 brought into the fibers over those oxidized in the muscular activity. If oxidation 

 diminishes, then fats will be deposited and the excess is expressed in the number and size 

 of the liposomes (fig. 8, pl.vi). 



The character of the liposomes, that is, their number, size, and arrangement in the 

 pink muscle depends also on one other very different group of factors. This is the struc- 

 ture of the muscle (fig. 13, pi. viii). That the fat is laid down in chains of liposomes of 

 the minute sizes that have been described must depend largely upon the structural 

 arrangement of the fibrilte and of the interfibrillar sarcoplasm. It is not desired, how- 

 ever, to discuss this factor beyond merely calling attention to it. 



