STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. 1 25 



presentation of the matter to consider the phenomena of fat mobihzation in these tissues 

 separately. I will take the simpler case first, i. e., the pink muscle tissue of the lateralis 

 profundis muscle. 



TRANSFERENCE OF F.\T IN THE PINK MUSCLE. 



Let the reader recall the characteristics of this muscle up to the time of the entrance 

 of the salmon into fresh waters, viz: (i) The intermuscular fat of the pink muscle is 

 slight in the early growing stage as represented by fish 10 to 15 cm. long which are 

 migrating toward the sea. The intermuscular fat increases in quantity after they reach 

 the sea, and reaches its maximum when the fish cease feeding — that is, when they begin 

 the adaptation process preparatory to entering the estuaries. (2) The intramuscular 

 fat is absent in the young salmon of fresh water, also in the voraciously feeding sea 

 forms, up to the time the salmon cease to feed, except for traces of fat in the smaller 

 fibers just at the end of this period. (3) The intramuscular fat after the beginning of 

 the spawning migration makes its appearance throughout the substance of the pink 

 muscle fibers of all sizes. It appears in short chains of very small liposomes that are 

 quite evenly interspersed among the groups of fibrillae of the muscle cells. This intra- 

 cellular fat is present within the pink muscle fibers throughout the migration and at the 

 time of death after the spawning. 



The special contrast is in the distribution of muscular fat just before and just after 

 the salmon cease to feed. The important change is in the relatively sudden appearance 

 of the Hposomes among the"fibrillce of the pink fibers. For this phenomenon the follow- 

 ing explanation is offered : 



Active feeding salmon are also rapidly growing salmon. While growth is taking 

 place all excess of fat is laid down in the connective tissue or in the dark muscle and 

 never in the muscle fibers of the pink muscle. The concentration of the fatty products 

 never exceeds the oxidations in the fibers of the pink muscle, hence no intracellular 

 deposit occurs." The transition from a feeding to a fasting state is associated with 

 numerous tissue changes in other parts of the body, changes which are accompanied by 

 equally important functional readjustments. Among the functional changes the one 

 that most concerns the present argument is the increased production of the fat-splitting 

 enzyme, lipase. Assume for the moment that the products of the last digestion have 

 been absorbed into the blood and have already been utilized by the tissues. Assume 

 also that this state has reached a point where the expenditure of energy must be done 

 by drawing on the body reserv^es. Then what can happen ? 



The salmon tissue glycogen is a negligible quantity. There is no adequate supply 

 in either muscle or fiver, as in the mammalia. Glycogenesis can not, therefore, come to 

 the support of the body in this crisis. 



There is an abundant store of fat in the intermuscular depot, great quantities of it, 

 and a lipogenesis * comes to the support of the salmon in a way quite comparable to the 

 glycogenesis of the mammal as conceived by Claude Bernard. Under these conditions 

 the activity of the muscular tissue is directly dependent on the fat as a source of energv. 

 The muscle oxidizes fatty bodies in the salmon, just as it oxidizes carbohydrate bodies in 

 certain other well-known animals. 



'I .\n exception may be found in the border zone of fibers between the pink and the dark muscle. 



b Loevenhart: On the relation of lipase to fat metabolism, lipogenesis. American Journal of Physiology, vol. vj. lyoi. p. 331. 



19371°— vol 33—1.5 9 



