Il8 BULLETIN OF THE BUREAU OF FISHERIES. 



liposomes. In some fibers they are uniformly distributed through the substance of the fibers; in others 

 there is apparently no fat in the middle of the fiber. In general, liposomes are present in the superficial 

 areas even in those fibers which have the least fat. The whole appearance suggests a nutritive balance 

 in which it is just a question whether all the fat will be used or whether there will be an excess sufficient 

 for deposit. 



The teased muscle shows great variation in the quantity of fat in tlie individual fibers (1/12 oil). 

 At the surface of the fiber is a good deal of fat in small droplets, the subsarcolemmal fat. The liposomes 

 in the chains are small like those in normal pink muscle. The number of chains is also low. In the 

 fibers carrying the least fat these chains are all but absent. 



Microscopic examination of the cheek muscle. — The muscle fibers of the cheek muscle are very com- 

 pactly arranged. In comparison with the Ilwaco type the fibers are less rotund in outline. The 

 histological structure is indistinct. In many fibers the fibrillac can not be seen because of a disintegra- 

 tion which marks the first stage of degeneration. Certain fibers scattered irregularly through the section 

 show a definite protoplasmic degeneration with vacuoles and pigmentation. The pigment granules are 

 small in size, o.i to 0.2 fi in diameter. They are unevenly distributed through the fibers and apparently 

 somewhat greater near the surface. There is great variation in the quantity^ of pigment in different 

 individual fibers. 



The fat in the cheek muscle is limited to a very few small groups of intermuscular fat. No traces 

 of fat could be distinguished within the fibers themselves. 



SIGNIFICANCE OF THE OBSERVED CHANGES OF THE AMOUNT OF FAT. 



It is obvious that the salmon fat furnishes the food during the migration fast. 

 The revelations of the microscope are convincing on this point, even if there were no 

 collateral supporting evidence. 



My unpublished chemical analyses of the tissues have revealed a dearth of carbo- 

 hydrates in the salmon tissues at all stages of the migration. This fact is of vital signifi- 

 cance in connection with the fat problem. The lack of carbohydrates and the abundance 

 of fats support Miescher's assumption that fats furnish the source of the muscular energy 

 expended by the salmon during the migration. In connection with a series of salmon- 

 feeding experiments " it was shown that the salmon liver exercises a distinct lipogenic '' 

 function during the feeding and growing stage. Noel Paton has found that the amount 

 of fat in the liver of the frog is increased after fat feeding."^ It seems to me that in 

 animals like the salmon the lipogenic function of the liver becomes a primary function, 

 taking a role quite comparable to that of the glycogenic function of the organ for many 

 mammals. Fishes of this class are carnivorous. Their food is of a highly oily character, 

 as is also that of certain birds, and is continuously so. The food is rich in proteins and 

 fats and in inorganic constituents, but it is poor in carbohydrates. In the adaptations 

 to such a diet, if for no other reason, the salmon has reached the point in its phylogenetic 

 development where fats furnish a direct and primary source of foods for the energy 



« Now in manuscript. 



' It was Loevenhart (American Journal of Physiology, vol. 6, p. 331, 1901) who first advocated the idea that we might have 

 a "lipogenesis" in the body comparable in character to the " glycosenesis" of Claude Bernard. He suggests that wherever there 

 is fat storage there will be lipase, and proves it by investigations on a niunber of tissues that contain fat. for example, the liver, 

 mammary gland, pancreas, brain, spleen, heart muscle, blood, adipose tissue, etc. He says: "In the case of fats the areolar tissue 

 is the great primary store, secondary deposits being found in all the tissues. In some animals even this difference in the storing 

 of fats and carbohydrates is not to be noted. In many fish, notably the cod, the liver, at certain seasons of the year, becomes the 

 great depository for fat. The liver we have found to possess powerful lipolytic activity, and hence, under proper conditions, it 

 should be capable of storing fat. Moreover, this is in accordance with the experiments of Noel Paton, who showed that the fat 

 contained in the liver of frogs is increased after a fatty meal. It is believed that both phases of lipogenesis are induced by 

 lipase, a fat-splitting and fat-forming cnzy-me. " From my observations I am convinced that lipogenesis is a definite and specific 

 function of the liver in certain carnivorous animals whose normal food consists of a high percentage of fat, as is the case in the 

 king salmon. 



<^ Paton, D. Noel: On the relationship of the liver to fats. Journal of Physiology, vol. xlx. 1S96, p. 167. 



